Urbanised Nature in the Past Site formation and environmental development Jens Heimdahl

Urbanised Nature in the Past Site formation and environmental development Jens Heimdahl
Urbanised Nature in the Past
Site formation and environmental development
in two Swedish towns, AD 1200-1800
Jens Heimdahl
Avhandling i Kvartärgeologi
Thesis in Quaternary Geology
No. 5
Department of Physical Geography and Quaternary Geology
Stockholm University
2005
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Cover painting by Jens Heimdahl
ISBN 91-7155-143-3
ISSN 1651-3940
Akademitryck AB
Urbanised Nature in the Past
Site formation and environmental development
in two Swedish towns, AD 1200-1800
Jens Heimdahl
This doctoral thesis has five appendant papers, listed below. They are referenced by their
roman numerals in the text. All figures included in the thesis are original illustrations made
by the author.
Paper I
Heimdahl, J., Menander, H., and Karlsson, P., in press: A New Method for Urban Geoarchaeological Excavation, Example from Norrköping, Sweden. Reprinted from Norwegian
Archaeological Review, Vol.38:2 (www.tandf.no/nar) by permission of Taylor & Francis
AS.
Paper II
Heimdahl, J.: Urban Sediments as Indicators of Changes in Land use and Building Tradition
in two Swedish Towns, AD 1200-1800 in two Swedish Towns. Manuscript
Paper III
Heimdahl, J.: Botanical Evidence of Changes in Vegetation and Cultural Landscape in PostMedieval Karlstad, Sweden. Manuscript
Paper IV
Heimdahl, J.: Botanical Evidence of Changes in Environment and Tradition in Norrköping,
Sweden, AD 1200-1660. Manuscript
Paper V
Heimdahl, J.: Archaeobotanical Evidence of Early Tobacco Cultivation in Norrköping,
Sweden. Manuscript accepted by Vegetation History and Archaeobotany
Content
1 Introduction
2 Interdisciplinarity
Geology and archaeology
Interdiciplinary urban research
Occupational layers and archaeological stratigraphy
Clashes in terminology
Stratigraphic terms used in this thesis
3 Urban occupational deposits
Urbanisation and towns
Urban deposits
Dark earths
The stratigraphy of urban constructions
Stratigraphy of waste
Urban pedogene soil processes
4 Urban plant ecology
Earlier studies of urban archaeobotany in
Sweden and neighbouring countries
5 Taphonomy of urban macro remains
1. Biology
2. Depositional processed and ecology in urban environments
A. The local flora
B. The regional flora
C. Plants from pastures and meadows
D. Cultural plants
3. Human influence
4. Preservation of plant macrofossils
5. The reworking processes
6. Sampling preparation and registration
7. Personal biases
6 Study sites
7 Methods
Norrköping
Karlstad
Fieldwork
Macrofossil analysis
Pollen analysis
Diatom analysis
Grain size distribution
Organic carbon and loss on ignition
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C-Dating
Other dating methods
Ecological grouping
Biological nomenclature
8 Summary of papers
Paper I
Paper II
Paper III
Paper IV
Paper V
9 Discussion
Urban strata, a formation model
The formation of dark earth
Sediments, soil horizons and culture
10 Conclusions
References
Svensk sammanfattning
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Abstract
In order to explore site formations and reconstruct environmental development in Medieval and Post-Medieval towns, urban occupational strata in Norrköping and Karlstad were studied according to biostratigraphy,
sedimentology and pedology. New field procedures including continuous pilot sampling, parallel archaeological and geological stratigraphic interpretation, and on-site analysis of plant macrofossils were developed and
applied at archaeological excavations in both towns. Representation of both disciplines in the field during
excavations greatly contributed to more complete field interpretations.
Stratigraphical analyses indicate that geological processes have been active in both towns, and reveal similarities in site formation. The earliest proto-urban phase is represented by the presence of dark earths, formed
by the combination of alluvial processes and cattle tramping. Alluvial processes were common in Karlstad
due to the flooding of the river delta, and in Norrköping due to the sloping topography. Both situations were
enhanced by human activity, which caused drainage problems. A significant change in composition and origin
of house foundation fill was also noted. The oldest foundations contained fine-grained material of local origin
in contrast to younger foundations, which contained coarser material, sometimes of regional origin. This is
interpreted as a professionalisation of the urban building tradition, which in Norrköping occurred during
the beginning of the 17th century and in Karlstad during the 18th century. Site formations of urban strata are
regulated by three major factors: deposition, post-depositional soil formation and erosion/truncation, which
all may occur both culturally and naturally.
Plant macrofossil analyses in Norrköping and Karlstad resulted in a fossil record with a total amount of
203 and 169 different types of plant species and taxa respectively. The records indicate that site formation
processes seem to have been inhibited during wintertime. The results also confirm the idea of the early Scandinavian towns as rural, also during the Post-Medieval time. The finds of cultural plants in Karlstad indicate
18th century cultivation of Fragaria moscata and 17th century import of Pimento officinalis. In Norrköping
remains of beer additives confirm that the tradition of combining Humulus lupulus and Myrica gale disappeared after the 15th century, but also indicate a the use of Filipendula ulmaria as a beer addative. Finds of
seeds from Nicotiana rustica suggests that tobacco cultivation occurred in Norrköping 1560-1640, which is
some decades earlier than known so far in Sweden.
Keywords: Urban stratigraphy, environmental reconstruction, site formation, geoarchaeology, dark earth,
macrofossil analysis
Urbanised Nature in the Past
1 Introduction
more carefully discussed in the chapter “Urban occupational deposits”.
The foundation of palaeoenvironmental studies of
urban areas is the interpretation of the urban stratigraphy. It is important to understand the site formation processes of urban occupational deposits, since
these deposits derive from both cultural and natural
processes. Ideally, archaeologists and Quaternary
geologists should perform the field interpretation
together. However, the archaeological method of recording and interpreting urban stratigraphy, developed during the last 25 years, has often proven to be
difficult and demanding to combine with the methods used by visiting geologists (cf., Lucas 2001).
The present thesis is based on site studies and analyses of samples collected from two urban excavations
performed within the frames of so called ‘rescue archaeology’. A rescue excavation is conducted as a
controlled form of the destruction of material that
is classified as cultural heritage when making room
for new constructions. The task of archaeologists is
to retrieve, document and interpret the archaeological remains, leaving a description and interpretation
in its place. Ideally the description should leave possibilities for researchers in the future to make new
interpretations. In Sweden rescue archaeology is financed by those responsible for the exploitation of
the ground where ancient remains are present. Economical frameworks defined by the county administrative board limit the excavation time and the analytical work performed after the excavation. It affects
also the choice of strata that are to be documented.
Generally urban occupational deposits in Sweden
that are older than the 18th century are considered to
be part of the cultural heritage and are classified as
ancient remains that should be preserved. Younger
strata are excavated without documentation.
Towns are often built on older remains called ‘urban occupational deposits’ that contain information about the history of the town. Geological and
biological remains are mixed and interbedded with
archaeological traces of houses, streets and artefacts
(man-made objects). In other words, urban occupational layers do not only contain ancient cultural remains, but also environmental archives from which
palaeoenvironmental records can be extracted. Urban nature occurs alongside and intermingled with
the cultural life in a town, and adapts to and affects
urban cultural expressions. In this way, the study of
urban nature results in the knowledge about urban
culture, and thus we may find examples throughout
history of the reactions and responses in the relation
between culture and nature.
Traditionally, the main focus of geological and biological studies have been placed on the ‘undisturbed’
nature – the nature untouched and unaffected by humans. In later decades, with growing concern about
the anthropogenic effects on the environment, studies of ‘disturbed’ nature have become more common.
Among culturally affected areas, the urban environment can be considered the most extreme. Geological and ecological studies of towns – urbanised nature – is however a young and growing discipline
(Gilbert 1989, McDonnell & Pickett 1990, Botkin
& Beveridge 1997, McDonnell 1997, Walbridge
1998, Nilon et al. 1999). In this field, studies of the
palaeoecological traces in urban occupational layers
may contribute new perspectives (e.g., Latalova et
al. 2003, Wittig 2004). The term ‘urban’, used in the
title of this thesis, has been defined in many different
perspectives, for example according to law, history
and demography. I use this term to characterize a
specific type of environment. The definitions will be
A
20
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B
Karlstad
County of
Värmland
Sweden
60
County of
Örebro
County of
Södermanland
Vänern
Norrköping
Baltic Sea
55
200 km
County of
Västra götaland
County of Östergötland
50 km
Figure 1: (A-B) location of the investigated towns of Norrköping and Karlstad in southern Sweden.
7
J. Heimdahl
The sites investigated within this study are situated
in Norrköping and Karlstad, middle Sweden (Fig. 1).
The main aims are: I) To develop methods for integrated fieldwork between archaeologists and Quaternary geologists/palaeoecologists (Paper I). How can
the members of the different disciplines adapt their
working procedures to utilize each other’s capacity
of interpretation? II) To reconstruct site formation
and environmental development at two urban sites
(Paper II-V).
Reconstructions of site formation and environmental development are performed according to two
main perspectives. Site formation is mainly studied
by sedimentology and pedology, an approach that I
refer to as ‘geoarchaeological’ (Paper II). Environmental development is principally studied from the
perspective of biostratigraphy/archaeobotany (Paper
III-V). However, the two perspectives of geoarchaeology and archaeobotany are sometimes integrated
to confirm or contradict specific results.
This thesis has been written from the perspectives
of Quaternary geology and palaeoecology/archaeobotany. The environmental development of Karlstad
and Norrköping has been previously studied from
the perspectives of archaeology and history, studies
which I take into account, and the conclusions of
which are compared with the results and conclusions
in this thesis. Hence, it is my intention that archaeologists and historians, as well as Quaternary scientists and botanists, should be able to understand, use
and scrutinize this research. Accordingly, the different disciplines require an introduction and my basic
approach to this interdisciplinary work is presented
below.
2 Interdisciplinarity
The description and interpretation of objects and
subjects may be facilitated if they are approached
from different disciplinary perspectives. Geological
deposits may contain biological remains and hence,
a biological perspective can contribute to the understanding of the deposit. The objects of the archaeological study are the remains of material culture,
which are also possible to study according to the
methods of natural sciences, history and social sciences.
These statements and examples may sound trite,
but while they are easy to make, they are, however,
difficult to implement.
Geology and archaeology
Since the disciplines of geology and archaeology tra-
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ditionally belong to different faculties, natural sciences and art, this may give an impression that they
are fundamentally different. It has been stated that:
“…archaeology […] straddles the gulf which separates the arts from the sciences.” (Hodder 1992). But
I don’t believe that it is so. I don’t think there is a
gulf.
A popular opinion concerning those differences is
that natural sciences are based on empirical principles and use quantitative methods while the humanities are based on hermeneutical principles and mainly use qualitative approaches. This is incorrect; the
fundaments of both disciplines rest upon empirical
principles and hermeneutics (sensu lato interpretation – not only of text) and use both quantitative and
qualitative methods (Kieffer 2005). For example, geological interpretation of stratigraphical sequences
is inherently hermeneutic and qualitative. Similarly,
the botanical identification of plant remain based
on morphology, is qualitative. These studies can be
quite subjective, perhaps more so than either discipline would like to admit.
There is currently a debate among Scandinavian
archaeologists concerning the question of what may
be considered archaeology (Svestad 2004; Wienberg 2004; Cornell 2005; Hegardt 2005; Herschend
2005; Karlsson 2005; Kristiansen 2005; Notelid
2005; Rundqvist 2005). It relates to the criticism
of post-processual archaeology, which emphasises
the symbolic meaning of material culture, partly as
a reaction to positivistic trends, the so-called ‘New
Archaeology’ that influenced archaeology in the 60s
and 70s and attempted to reform archaeology to become more like the natural sciences. The debate is
ongoing and trends are developing in all scientific
disciplines but I would like to emphasise that my
studies of archaeological material from a perspective
of natural science are not to be seen as a contribution
to this debate. I will not debate the nature of archaeology, only some of the study objects of archaeology,
although from a different perspective.
Some of the differences between humanities and
natural sciences fall back on the classic and controversial question of what is considered nature versus
culture. One perspective is that humanity exists beside or on the top of nature and that human activity (culture) is considered separate from nature. The
contrasting perspective is that humanity is part of
nature and that culture should be considered as a
part of nature as well.
The controversial aspect of these questions partly
derives from the definitions of the terms that apply
to societal values. ‘Nature’ is often used as synonymously to positive terms such as ‘normal’, ‘ordinary’,
Urbanised Nature in the Past
Figure 2: Conceptual model of
how an object – urban occupational strata and the processes that
caused them (marked with grey)
– may be studied by different disciplines. More disciplines may also
be added, such as chemistry, physics and human geography. These
disciplines may further be divided
into sub-disciplines e.g., geoarchaeology which is at the boundary zone between archaeology and
geology.
‘usual’, ‘regular’ or ‘original’, and to describe something that is ‘good’, ‘harmonious’ or according to a
higher or ‘God-given’ purpose. On the other hand,
the term ‘culture’ is more complex, referring to a
way of life, customs, beliefs, art, identity etc. It may
refer to something sophisticated but also something
that opposes nature – something ‘unnatural’.
From the perspective of natural science, humanity might also be seen as a part of nature because
humans and human culture are observable in the
physical world. This does not mean that all aspects
of humanity and culture can or should be studied
according to the methods of natural science. In fact,
most cultural aspects are far too complex for these
methods and instead, require methods from the humanities and social sciences. In the following, I will
use the term ‘culture’ to describe human activity
while ‘nature’ will be used for everything that is not
cultural. It is merely a practical use that results from
the need to separate human actions from non-human
actions, not a moral statement. In this regard, it is
also important to note that irregardless of whether
we include culture as part of nature or not, nature
and culture strongly affect each other and often in
such a way that cause and effect are difficult to distinguish. It is not always possible to separate nature
and culture, and it is in such cases that interdisciplinarity is put to the test.
Interdisciplinary urban research
A multidisciplinary approach is to study an object
from the perspective of many different disciplines
parallel to each other. This multidisciplinary work
becomes interdisciplinary in the dialogue between
the different disciplines, and when they thereby af-
fect and influence each other.
In this study the objects consist of the physical remains of towns – urban occupational strata. These
strata, and some of the processes that have caused
them, may be studied from the perspectives of archaeology and natural sciences. However, some of
the causes behind the processes may be of such nature that they only can be understood by the use of
historical or sociological methods, even if the physical object itself cannot be explained according to
those methods (Fig. 2).
Since the end of the 19th century, urban occupational deposits have been considered part of our
cultural heritage and the main responsibility to investigate them has fallen on archaeologists. European towns generally belong to the period defined as
‘historical’ – the period that can be studied through
written sources. When archaeologists began to study
the material from this period they collaborated with
historians. The archaeological branch that studies
remains from the historical period is called ‘historical archaeology’, and it has to consider different
types of sources of information. The specific study of
town remains may be called ‘urban archaeology’. In
Sweden urban archaeology includes ‘Medieval’ and
‘Post-Medieval archaeology’, two periods that are
separated by the time of reformation of the church
defined at AD 1527 by king Gustavus Vasa. Urban
archaeology has undertaken many questions that
traditionally fall within social sciences and human
geography, questions important to the urbanisation
process.
Many archaeologists remedy the need for multidiciplinary knowledge by taking supplementary training
in Quaternary geology, and there are archaeologists
that are also good geologists or geoarchaeologists.
9
J. Heimdahl
This supplementary knowledge is however not
enough to cover the need at all excavations.
Archaeologists and geologists work with different
scientific questions, not only because of the differences in the study objects, but also because of the
differences in disciplinary background. Archaeologists need not only to determine what process or behaviour has formed a certain record, but must also
ask questions about why this process or behaviour
occurred and attempt to understand the context of
social interaction behind it (cf., McLees et al. 1994,
Larsson 2000). Geologists need to ask questions
about the mechanisms behind processes but since
those processes traditionally do not include human
activity, social interactions are not normally considered as a factor. If a geologist works with occupational layers, the processes behind these layers may
be caused by social interactions and should therefore
be considered. However, since geologists generally
lack the necessary knowledge concerning cultural
explanations, the interpretation process should be
performed in conjunction with archaeologists or/and
historians (Fig. 2).
Occupational layers and archaeological stratigraphy
The sediments that compose the stratigraphy in occupational sites may be of natural or cultural origin.
Natural deposits that can be formed within, or cover
an occupation may be of eolian (wind transported),
alluvial (water transported) or colluvial (gravity
transported) origin but most common are depositions
created by humans. Such deposits are called ‘occupational layers’, ‘occupational deposits’ or sometimes
‘cultural layers’. It is here worth mentioning that the
geological terminology concerning occupational deposits is poor. On the maps of Quaternary deposits
published by the Geological Survey of Sweden (SGU),
urban occupational layers are marked as “Artificial
fill: the original ground surface is covered by an alien
material” (Persson & Svantesson 1994). The word
‘alien’ may here also serve as an example of how
humans sometimes are viewed from the perspective
of geology. The archaeological terminology is hence
developed independently from geology. A general
difference between geological and archaeological
stratigraphical methods is that those used by archaeologists, to a greater extent, are focused to describe
the surfaces buried within the stratigraphy (contacts
between layers called ‘interfaces’). Geological terms
and methods are more focused around the layers and
sediments themselves and their changes with depth.
Different definitions of ‘occupational layer’ exist,
partly because field-terminology varies locally and
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Figure 3: Many excavations during the first half of the
20th century were performed according to the ‘Box and
baulk system’. The excavations were performed according to a regular system of rectangular areas. The bottom
of the pits was always horizontal and often cut through
strata that were dipping. Stratigraphic control was poor
and stratigraphic interpretation difficult.
also because of the methodological development
within stratigraphy. Traditionally there has been a
need for archaeologists to separate stratigraphical
units formed intentionally, like fill used as foundation for houses or other buildings, from units that
are formed unintentionally, either by cultural or
natural action. Strata formed intentionally may in
fact be considered as artefacts (cf. Arrhenius 1996)
since humans create them, and their form and placement may reveal information about the people that
formed them. On the other hand, strata formed unintentionally, for example as a secondary effect of a
cultural activity, may reveal information about this
activity also by its content.
Excavation techniques differ slightly between
countries and regions. Here I will briefly describe the
development of excavation methods in Sweden. They
have many international connections, especially to
the development in Britain (cf., Roskhams 2001).
For a long time excavations were made in rectangular, horizontal blocks, the so-called “box and
baulk system” (Larsson 2000, Roskhams 2001),
without concern for how the layers dipped (Fig. 3).
The stratigraphy was carefully documented by the
interpretation and drawing of sections when the
excavation was completed, but the stratigraphical
control of the finds was poor. During the 1970s, the
stratigraphical awareness started to grow among urban archaeologists who had begun to confront the
complex occupational deposits of towns. Järpe et al.
(1979) suggested a drawing standard for documenting occupational layers. Also a narrow definition
of what was to be called ‘occupational layers’ was
suggested, according to the idea that the strata had
“grown” through “unintentional cultural sedimen-
Urbanised Nature in the Past
tation”. Beside those slowly and continuously deposited sediments called ‘accumulations’ (Sw. avsatta
lager), there were also intentionally created layers
called ‘depositions’ (Sw. påfö
f rda lager), which were
fö
not to be considered occupational layers. The idea
was that the unintentionally accumulated occupational layers that successively had been growing during occupation (due to the habit of waste handling)
would contain more information about the everyday
life on the site than the intentionally formed deposits. Järpe et al. (1979) also called this type of occupational layers ‘cultural gyttja’ and presented a
number of symbols, representing different types of
layers, to be used use within section drawing (Fig.
4). The type of layers presented in the system were
however not explained and defined, and even though
many of the words used (such as ‘peat’, ‘gyttja’, ‘alluvial layer’ etc.) were of geological origin, it is obvious that the definitions used by the authors were not
geological. For a period the paper by Järpe et al. and
the symbols they presented had a great influence on
stratigraphical methods in Sweden (Larsson 2000,
Tagesson 2000a) since it contributed a tool to handle stratigraphy in a more interpretative way. It also
seems to have corresponded to former ideas about
site formation process in Britain (Matthews 1993).
During the 80s Andrén (1985, 1986, 1989a, b)
introduced the terms ‘latent’ and ‘manifest’ which
aimed to separate deposits formed due to unintentional action from those formed by intentional acts.
Since the different deposits are formed according
to different degrees of intent, they have to be separated and sometimes interpreted in closed contexts
(cf. Andrén 1989a, b). The ideas of different degrees
of intent in site formation processes have also been
discussed by Florén and Dahlgren (1996) who suggested a separation between ‘acts’ (intentional acts)
and ‘behaviour patterns’ (acts according to habits
without specified intention).
The need for better stratigraphic control within urban archaeology was emphasised by Beronius-Jörpeland (1992) and a broader definition of occupational
deposits was suggested. She suggests that all deposits
created by humans are to be called ‘occupational deposits’, and stressed the importance of separation between depositional and post-depositional processes.
During the 80s and 90s there was a continuous development of excavation techniques, although they
differed locally. The technique of excavating stratigraphically was developed. One stratum at a time
was excavated and the extension of the stratum was
followed horizontally. By this method it was possible
to uncover and separate old ground surfaces, which
made the interpretation of the site development easi-
er (e.g., Anund 1995, Ros 1996, Larsson 2000).
A considerable shift in excavation techniques, especially at urban sites, occurred in the beginning of
the 21st century. The shift had its prologue in 1993
when the method of so-called Single Context Recording (hence referred to as SCR) was introduced
in Sweden after experiences from Norway (Larsson 1993). SCR is a stratigraphic recording method
adapted to archaeology that deals with complex
stratigraphy. It was developed in Britain by Edward
Figure 4: Stratigraphical drawing according to the system
of Järpe et al. (1979). According to this system only the
‘accumulated’ units and the ‘cultural gyttja’ are considered
as true occupational layer. The system presented a large
number of symbols for the different types of material, but
did not define the material itself. A comparison of different
stratigraphical records obtained with this system, shows
that the terms are not classified according to any geological or archaeological definition.
11
J. Heimdahl
Fig. 5: Example of application of Harris matrix (Harris 1979). In the matrix to the left stones are marked with boxes,
layers with rings, holes with pentagons, and hole infillings with triangles. In this case, layer (4) is the settling sand for the
cobblestones (3). If this cobbled ground were interpreted as a part of the construction that was held up with posts, e.g. a
shed, posthole (2) would also be a part of the shed-context, marked within the dotted line in the matrix. The hole infilling
(1) is a later deposition and will not be a part of the context.
Harris (Harris 1979 and Harris et al. 1991) and was
built on the idea of classifying and uniting different
stratigraphical units (which are defined as consisting of ‘depositions’ and ‘interfaces’) and artefacts
into time dependent contexts. The contexts are in
turn connected to groups. The stratigraphical relation between those units, contexts and groups, are
illustrated by the drawing of a so-called ‘Harris Matrix’ (Fig. 5). This type of matrix was used earlier, for
example at Helgeandsholmen in Stockholm but the
excavation only used parts of this method (Broberg
& Douglas 1983). In this method both layers, interfaces and “negative” units, such as holes, are given
the same treatment. The method has proven to be a
powerful and effective tool in order to document and
interpret stratigraphical information, and it forces
the user to carefully consider all strata and contacts.
SCR has dominated urban excavations in the latest
years, for instance at excavations in Lund from 1993
(Larsson 1993, 2000); Norrköping 1998 and 2000
(Hållans et al. 1999, Tagesson 2000b Karlsson et al.
in press); Sigtuna 1999-2000 (Fogelberg & Wickström 2003) and Karlstad 2001 (Bäck 2002).
There has been criticism against the weaknesses
within the SCR-system, for example the problem of
catching the cultural activities within the time-gaps
between the stratigraphical units described within the
matrix (Fogelberg et al. 2004). Harris (1979) states
that occupational layers consist of two components:
depositions and interfaces. In the later years, the
need for separating the strata into depositions and
soil horizons (depositional and post-depositional
remains) within the interpretation has been stressed
(Heimdahl 2003, 2004). The depositions generally
reflect short-term events, while soil horizons devel-
12
oped within the depositions are generated by the effect from a longer sequence of every-day activities.
In later years, the development of digital tools and
GIS-techniques have greatly improved urban stratigraphical documentation and new techniques are
tested alongside the use of SCR. Extensions of layers and positions of finds and samples are measured,
digitalised and registered in GIS-programs (for example Arc-View). Also 3-D visualization of complex
urban stratigraphy has been tested, for example in
Naantali, Finland (Lehtonen & Uotila 2004).
The extensive redeposition that has occurred in
urban occupational deposits sometimes makes it difficult to interpret finds therein. This has led to a need
to classify different deposits according to the risk that
its content (of for example artefacts) is redeposited.
In Britain, a system of classifying finds into ‘primary’
(original) and ‘secondary’ (redeposited) positions has
been in use, but was criticised by Roskhams (1992)
as being too coarse. He instead suggested a system of
four classes, relating the find to chronological, spatial and functional contexts. In Sweden, this system
developed into a three-grade scale where the finds
are classified as:
• primary deposited – according to original time,
space and function contexts, for instance household
tools dropped on the floor in the house where it was
used.
• secondary deposited – contemporaneous but isolated from original context in function and space, for
example waste deposits.
• tertiary deposited – redeposited material, isolated
in time, space and function (Larsson & JohanssonHevren 1998), for example material and artefacts in
Urbanised Nature in the Past
layers that are excavated and used as fill in new constructions on another site.
This system was later adapted to account for the
depositions themselves (Tagesson 2000a). Tertiary
deposits consisting of fill that is redeposited may
then have had a primary function, for instance as a
foundation for a house.
Clashes in terminology
When discussing terminology, we must assume that
terminological use within a discipline often differs
between different groups of researchers, both locally
and regionally. However in this discussion, I refer to
geologists and archaeologists, although simplified, as
two homogeneous groups and discuss some similarities and differences that appear to be widespread.
Both geology and archaeology work with the physical material that holds information on past conditions, and both disciplines attempt to gain knowledge
through the use of stratigraphic principles. Many of
the stratigraphic terms used in archaeology derive
from geology (c.f., Larsson 2000). It can therefore
be presumed that archaeologists and geologists use
the same stratigraphical terminology. This is partly
true, especially when it comes to descriptive terms
(e.g., ‘deposition’, ‘interface’) and technical terms
(e.g., ‘gravel’ or ‘clay’).
However, there are major differences between the
uses of terminology in the two disciplines. Archaeologists usually do not apply many terms used in geology. Examples are: ‘autochthonous’/‘allochthonous’
and ‘concordance’/‘discordance’, which are descriptive terms that probably would be useful also to archaeologists. Although when these terms have been
used by archaeologists (e.g., Roslund 1997), other
archaeologists have found them complicated (Larson
& Johansson-Hervén 1998).
In other cases, archaeologists have developed their
own terms to describe stratigraphy. Good examples
are the terms referring to SCR and the use of Harris matrix. There are also examples of terms that
are used by both disciplines but differ in definition.
Some of those differences are necessary and depend
on the differences in approach, objects of study and
methods.
The different use of terms has led to interdisciplinary misunderstandings and conflicts. Since geologists often have a clearer view of terms associated
with sediments and soils, sometimes archaeologists
just leave it up to the geologists to classify the material. This can create a false sense that the material is
classified according to strict and correct principles.
This is perhaps so, but sometimes geological termi-
nology is insufficient to describe the material that
occurs in archaeological contexts, and the geologist
may lack knowledge of the formation process of “archaeological” strata. Also, terms with common definitions used in archaeology may at times be more appropriate than geological or pedological terms when
describing occupational deposits (cf., Heimdahl et
al. 2003).
One example is the Swedish word torv, which has
two possible translations in English: ‘peat’ and ‘turf’.
In Swedish geological terminology torv is defined
strictly as ‘peat’ – an autochthonous accumulation of
plant remains, for instance vitmosstorv (Sphagnum
peat) or starrtorv (Carex peat). However, an older
meaning of the word, probably of agrarian origin, is
the uppermost vegetative zone of soils in grasslands –
the root horizon (easy to cut with a spade to sods) of
turf. In Sweden as in many other European countries,
turf has been used as a building material, for example in ramparts, earthwork and as a cover on house
roofs. At some archaeological sites, ground vegetation and root horizons may be covered and become
preserved as buried horizons within the stratigraphy,
which also may be considered turf. Furthermore different types of peat have been used throughout history. For instance, Sphagnum was used as a packing
material, as ‘toilet paper’, as moist buffering material in beds and as litter in stables (Krzywinski et al.
1983, Geraghty 1996, Hansson & Dicksson 1997).
In some cases, when a site is located in a moist area
(for instance an alluvial valley), peat may also have
accumulated naturally in the urban environment.
It is possible to find both remains of peat and
turf in urban occupational layers and of course, it
is important to separate these two different types of
material since they indicate different environmental
origin and cultural use. This does not mean that the
Swedish term torv should be applied only in one way
but it is of great importance to be aware of the different definitions in order to clarify descriptions.
Another example of confusing terminology is the
Swedish term jordart, which may be translated to
‘regolith’ – an unconsolidated deposit. It may have
both a genetic definition like ‘till’, ‘glaciofluvium’,
‘littoral sand’, or a descriptive function, for example ‘gravel’, ‘sand’ and ‘clay’. Occupational deposits may also be referred to as a type of jordart. In
Scandinavia, deposits of this type are of Quaternary
origin but the term is also used to describe weathered
material that may be much older in other parts of
the world. The geological term jordart should not be
confused with the pedological term jordmån, which
corresponds to ‘soil’ – the upper part of a regolith
that has been affected by post-depositional proc-
13
J. Heimdahl
esses associated with physical, chemical, biological
or cultural factors. The problem is that the English
term ‘soil’ is not only used in the strict pedological
definition but also in a more general manner, even by
scientists. It does not then refer to a specific type of
soil but either to all soils covering the world’s land
area (Brady 1990), or at times to the material composing a soil or terrestrial sediment. This use may
correspond to the word jord, which lacks a geological definition, but may sometimes refer to what in a
geological definition should be considered a regolith
(jordart). It may also be added that the term ‘earth’
is not used as a substitute for soil.
Many Swedish archaeologists are not aware of this
complexity of definitions and do not notice when a
British or American author refers to the pedological definition of soil or merely uses the word in a
general, undefined way. For instance, it is common
that archaeologists define culturally affected soil horizons as ‘occupational layers’. Since ‘layer’ refers to
a deposit, and the culturally affected soil to the main
part consisting of the minerogenic sediment that has
been there before the occupation, this often leads to
misunderstandings.
Torv and jord- (art/
art mån) are two examples of how
art/
problems concerning geoarchaeological terminology
may arise. These, and many more examples not mentioned here, reveal the importance of awareness of
the differences and similarities between the terminologies used within the two disciplines. Clear and open
communication between the disciplines is necessary,
not only through an explanation of terms, but also
through a sensitive and receptive dialogue.
Stratigraphic terms used in this thesis
The urban occupational layers I have worked with
are composed of two main physical units: depositional layers and post-depositional soil horizons.
Since it is of great importance to keep these apart,
I will use the terms sensu stricto according to the
working definitions presented in Table 1.
3 Urban occupational deposits
Urbanisation and towns
Historians, human geographers and archaeologists
have mainly performed research on the history of
towns during the last 25 years. Before the 1970s,
historians dominated the arena of urban science and
at that time very few urban archaeological excavations had been performed in Sweden. Exceptions
were the towns of Birka, Lund and Gamla Lödöse,
14
where long traditions of urban archaeology existed.
Large building projects during the 1970s and 1980s
caused a huge expansion in urban archaeology. As
a response to the need for information concerning
ancient remains in towns, a project called ‘The Medieval Town’ (Sw: Medeltidsstaden) was initiated by
the National Heritage Board (RAÄ). The aim of this
project was to provide an overview of the urban medieval remains in Sweden, which concerned about 70
towns that were given privileges before the Reformation in 1527 (Forsström 1982, Andersson 2001,
Lindeblad 2002).
The history of towns differs according to the definition of ‘town’. In the juridical aspect, a town is an
area that has received special privileges to regulate
trade. In Scandinavia, this system was first introduced in Denmark (11th century) and Norway (12th
century). Therefore, the oldest Swedish towns, according to this definition, are located in areas that
previously belonged to those countries. Lund and
Helsingborg in the county of Skåne was founded in
Denmark during the end of the 11th century. Kungahälla in the county of Bohuslän was founded 1130
in Norway. In Sweden, the system of town privileges
was introduced during the early 13th century. Examples of early Swedish towns, according to this definition, are Visby, Söderköping and Sigtuna (Ahlberg
& Redin 1994).
Another type of definition of town is social and
structural, for example “a dense settlement, where
inhabitants form a social unit in economic or/and
juridical aspect according to common interests in
trade” (Schück 1926). According to this definition,
Scandinavian towns are older. Ribe in Denmark
seems to have been founded as a central trading
place in the early 8th century. Birka in Lake Mälaren
(Sweden) existed c. 760-1000 AD, and many of the
later medieval towns seem to have been founded
upon older occupations, which in many cases may be
called towns, for instance Visby and Sigtuna. Within
the juridical definition of towns, those types of settlements are sometimes referred to as ‘proto-towns’
(Holmqvist-Olausson 1993).
Definitions related to the environmental aspects of
the terms ‘town’ and ‘urban’ are also used among
urban ecologists (cf., Mcintyre et al. 2000). In urban ecology, the environment is often compared
with rural areas along so-called ‘urban – rural gradients’ (e.g., McDonnell & Pickett 1990, McDonnell et al. 1997, Simmons et al. 2002, Moffatt et
al. 2004). ‘Urban’ and ‘rural’ are then commonly
defined according to population density in specific
areas (e.g., McDonnell et al. 1997). Urban palaeoecology often confronts similar gradients, although
Urbanised Nature in the Past
Table 1: Explanation of stratigraphical terms used in this thesis
Term
Contact and Interface
Dark earth
Explanation
The boundary between layers/beds/deposits. Archaeologists most commonly use ‘Interface’ while geologists use ‘contact’.
A dark, organic rich stratum (generally over 2 dm thick) that commonly pre-dates the well stratified medieval and post-medieval urban occupational deposits in Scandinavia and Europe. Dark earths are more
thoroughly discussed in Chapter 3.
Deposit, layer and bed
The terms are used synonymously for depositional units or sediments of natural or cultural origin. The
material in layers and beds may have been deposited during a single event or by successive deposition,
for example in water bodies where sedimentation of single beds may take some time. Layers, beds and
deposits can be divided into subunits that are also called layers, beds and deposits.
Facies
A series of specific stratigraphical units developed during similar conditions (cf. Reading & Levell 1996).
The stratigraphy at the sites studied here is divided into four different Facies. A Facies may further be
divided into subfacies.
Horizon or soil horizon
A post-depositional feature developed within a deposit/layer/bed by pedogenic processes under the
influence of climate, soil chemistry and/or biology. Horizons in urban occupational layers are often developed by tramping by humans and cattle. When horizons are formed through several strata, contacts
between layers can be destroyed and older stratigraphical features disappear or become obscured.
Phase
A term used by archaeologists (based on e.g. different building styles or other cultural habits reflected by
artefacts) to separate time dependent units in a stratigraphy
Sediment
Transported and deposited minerogenic and/or organic material consisting of one or several layers.
Soil
Not used as a single word in this thesis in order to avoid confusion. It is, however, used to describe postdepositional process or strata e.g., soil horizon, soil process or soil bioturbation.
Stratum and unit
Refers to an unspecified stratigraphical unit that has not yet been classified as a layer/bed/deposition or
a soil horizon or a combination of both.
Urban deposits
occurring chronologically, but there is generally a
lack of information concerning population density.
The term ‘urban’ is instead used to name a certain
type of environment with specific characteristics.
Early Scandinavian towns generally had a strong rural character since farms were often situated within
the towns. This means that the early urban environments had rural character that eventually decreased
and disappeared. Because of this process, the terms
‘urban’ and ‘rural’ are not mutually exclusive (cf.,
Clark 1992). I will use the term ‘rural’ as referring
to an environment dominated by activities occurring
in a rural economy (as crop processing and live stock
handling), n.b. the degree of self-sufficiency not defined. The term ‘urban’ will refer to a densely and
permanently populated area that is environmentally
characterised by trade, craft and/or industry.
A central issue within urban history is the processes that give rise to the towns – the urbanisation.
The causes behind urbanisation are complex. They
include geographical, social, historical, economical
and physical factors. Ambitions of a central political
power often seem to have initiated the process. In
Scandinavia, urbanisation occurred irregularly from
the late Iron Age (Viking Age) until modern times
(Andersson 2001).
The character of urban occupational strata in Scandinavia differs not only between but also within the
towns themselves. Compared to geological deposits, an urban stratigraphical unit varies on a smaller
scale due to its cultural origin. Of course there are
also many urban sites that lack older occupational
layers, both because of uneven deposition and as an
effect of truncation.
According to my own observations at urban excavations (in Norrköping 2000; Sigtuna 2001; Stockholm 1999, 2001; Lund 2003; Mariestad 2003; Karlstad 2003-2005 and Skänninge 2003-2005), as well
as studies of records from older excavations (Beronius-Jörpeland 1992, Larsson 2000), some general
features may be recognised.
Urban sites are commonly located close to the
water (for instance, rivers, lakes or in coastal areas)
since waterways were the natural routes for trade
and transport. As a result, many towns have been
exposed to flooding and alluvial deposits are often
found interbedded within urban deposits. Waterlogging of deposits is also common, which leads to
anaerobic conditions. This inhibits the decay of uncharred organic material and leads to the preservation of organic material, for example plant remains.
The thickness of urban occupational deposits
15
J. Heimdahl
Figure 6: Type profile of occurrence of older urban occupational deposits. They tend to be concentrated to depressions in
the natural substratum and as slope front fills. Older urban occupational layers are generally covered by modern fill, and
excavations occur where this modern fill would replace them.
seems to be dependent on local topographical features and therefore have a levelling effect on the urban topographical landscape, since they tend to fill
depressions and become thinner on the top of hills
(Fig. 6). In a flat landscape, the thickness of urban
deposits is generally even. In Sweden, the thickness
of urban deposits is up to 12 meters thick, excluding
19-21st century fills.
In many towns there is a general trend in the degree
of stratification according to relative age. Younger
units are generally thinner and more distinctly stratified than older units, which are often composed of
thick (20-70 cm), dark, homogeneous strata rich in
organic matter. Such old strata have proven difficult
to interpret through archaeological methods. Internationally they have been called ‘dark earths’ (more
thoroughly discussed in the following section). The
upper, well-stratified strata are generally easier to interpret since they mainly consist of two main units:
remnants of constructions (e.g., fills, houses and
streets) and waste.
The material that constitutes urban deposits varies from minerogenic to more or less organic but is
mostly a mixture of minerogenic and organic components. Charcoal, fragments of wood and faecal
material from both humans and animals often dominate the organic component. Reworking processes
were extensive, both due to deliberate actions such
as digging and truncation, and unintentional effects
of tramping by humans and animals. The material in
the deposits is therefore often from different origins.
Dark earths
The term ‘dark earth’ (in some early texts referred
to as ‘black earth’) originates from Britain and was
coined to describe the thick, homogeneous, poorly
stratified, dark soils that often separate the clearly
stratified urban deposits of the Roman and Medieval
Ages (Fig. 7). The term was traditionally associated
with the abandonment and decline of urban environments during the early Middle Ages – the ‘Dark Ages’
c. AD 500-1000 (Norman & Reader 1912). Dark
earths were formed as a result of cultural activities
16
that occurred at former urban and proto-urban sites
(Macphail et al. 2003). (Note that both ‘dark earth’
and ‘black earth’ are terms also used in the classification of natural Amazonian soils and humid step
soils. Those natural soils have nothing to do with
the dark earths found in the archaeological contexts
discussed here.)
In later decades archaeologists in, for example Italy, Belgium and France (terres noires) have adopted
the term. The European use of the term gave rise to
a broader definition, and ‘dark earths’ are no longer
considered to have been formed during a specific time
period, in a specific urban environment, or by a specific human activity. The term is now more generally
used to describe dark, thick (often 20-70 cm), poorly
stratified stratigraphic, organically rich units that occur at archaeological sites. The genesis of dark earths
on different sites is probably diverse. When occurring at urban sites, dark earth is usually associated
with some type of urban decline, and the local environment is often interpreted as changing into waste
ground or midden (Macphail et al. 2003).
Ideas about the processes that create dark earths
have varied. Macphail (1994) showed that dark
earth might be formed by natural soil formation due
to total abandonment of the area. A ruderal flora
may begin to grow in the house debris, giving rise to
entisols or inceptisols (developed by earthworm and
root bioturbation) in occupational deposits. Cattle grazing (Gebhardt 1997), middening (Macphail
1994), cultivation (Gebhardt 1997), market activities (Reece 1980), ‘backyard activities’ (Gebhardt
1997) and natural flood events (Corty et al. 1989)
have all been used to explain the formation of specific dark earths.
In the 1980s and 1990s, a discussion took place in
Italy concerning the formation process of dark earth.
The question was whether the formation process occurred during a few years or decades, or longer time
periods of hundreds of years (Macphail et al. 2003).
In later years, it has been obvious that dark earth
often reveals a more complex stratigraphy, obscured
by the bioturbation (e.g., Sidell 2000).
In Sweden, the term ‘dark earth’ has so far not been
Urbanised Nature in the Past
adapted in this European aspect. The term svarta
jorden (‘black earth’) has long been used to describe
soils with occupational remnants rich in carbon
dust, for example the soils in the area of the Viking
Age town Birka on Björkö in Lake Mälaren. Use
of this term is documented from 1683, probably as
an adaptation to the terminology used locally (Haldorph 1683, Hyenstrand 1992). After this, and since
the excavations during the 19th century (e.g., Stolpe
1871-1879), the term ‘black earth’ has been regularly used when referring to the complete stratigraphy
of the occupational layers in Birka (c. 1-2 m thick).
Also, well-stratified units preserved within the occupational layers at Birka are referred to as belonging
to the ‘black earth’. The Swedish term svarta jorden
is also used to describe the carbon-rich occupational
layers of the 12th century town of Kungahälla (Andersson & Carlsson 2001). Engelmark (2002) used
the term ‘dark earth’ for the urban occupational layers at Sigtuna, deposited between the 10th and 13th
century. Those layers are, however, well-stratified
units of urban occupational layers so in this case, the
term is used in a different way. In Norway, the term
‘black earth’ has been used to describe the remain-
Figure 7: Typical stratigraphical position and habitus of
dark earths in Britain (left) and Scandinavia (right).
ing deposits of the Viking Age marketplace Kaupang
(Sørensen et al. 2002). The term ‘black/dark earth’ in
Scandinavian contexts seems to refer to carbon/organic-rich urban occupational deposits in general.
Thick, poorly stratified, organic-rich strata that
predate well-stratified medieval urban units are also
commonly found in Scandinavia (Fig. 7). Apparently, they correspond to the European dark earths but
have not been referred to as such. In the following,
I refer to these Scandinavian units as ‘dark earths’,
in the broad, descriptive sense not connected to any
specific formation process or human activity. The
occurrences of dark earths have also been debated
in Scandinavia, but since this area lacks the traces
of Roman occupation as on the European continent
and on the British Isles, the Scandinavian dark earths
have generally been looked upon as indications of
a new development – a development that preceded
the advanced medieval urban phase, rather than as a
decline of an earlier advanced phase. To explain the
shift from dark earths to well-stratified urban units,
the focus has mainly been placed upon the changes
in the thickness of the strata.
The Scandinavian discussion concerning the dark
earths has generally been focused on their disappearance. Many Scandinavian authors note that this type
of thick occupational strata was formed between the
10th and 14th century (e.g., Andrén 1986). BeroniusJörpeland (1992) suggested that the high ‘growthrate’ of deposits, resulting in thick occupational layers, might indicate that settlement expansion was
at its height during this period. Runer (1999) noted
the difference between urban and agrarian development during Medieval time. While the occurrence of
thick urban strata decreases from the 14th century,
they seem to remain in many agrarian environments,
which are interpreted as an indication of a ‘social integration’ into new hierarchies that occurred within
towns but not in rural settings. In Lund and many
other towns, the thinning of occupational strata
from the 14th to the 17th century has been described
as a decrease in ‘growth-rate’ (Andrén 1986). The
thick, early occupational strata in Uppsala have
been explained as being caused by a ‘semi-agrarian’
economy with large cattle stocks within the town
(Ersgård 1986). The shift to thinner strata in Visby
is explained by the increase in waste control (e.g.,
Westholm 1990, Nydolf et al. 1992). Also Andrén
(1986) refers to the changes in waste handling when
explaining this general shift within urban occupational stratigraphy. The increasing use of manure on
fields during the 15th century may have decreased the
amount of cattle faeces deposited within the urban
environment, and the increasing use of pavements
17
J. Heimdahl
and permanent plots may have made it easier to keep
the town clean. Andrén also suggests that the wastehandling shift may indicate a changed cultural view
on waste. This view was supported by Solli (1989)
who suggested that the shift in the thickness of urban
strata in Norwegian towns was caused by social and
political changes. Accordingly, the ‘growth of layers’
may be a measure of a town’s capacity for organisation.
It is interesting to note the differences and similarities between the Scandinavian and European discussions concerning dark earths. One of the main
differences is what is considered status quo in the
environment where dark earth is formed. At many
urban sites where Roman towns preceded Medieval
towns, the interlayering dark earth is considered as
a break in an urban activity continuum. Apparently
pedogenic processes acting on the debris of Roman
buildings formed dark earth at some sites. Others
have been formed by rural activities (Macphail et
al. 2003). In Scandinavia, dark earth seems to indicate new development at a site. Apparently they are
formed during the initial phase of the riddling urbanisation process. Naturally, this phase has never been
referred to as an ‘abandonment’ or ‘decline’ – rather
the opposite – since the preceding environment commonly has been a non-occupied site, even though the
later urban phase with its thinner and better-defined
stratigraphical units is considered to be formed during a more advanced phase.
The similarities in these discussions are found in
the ideas concerning specific activities and processes that may have caused the formation of dark
earth. Cultivation, grazing/cattle handling, middening/waste ground use or less intensive occupational
activities have been common interpretations in both
the European and the Scandinavian debate.
The methodological approach to dark earth and
obscured stratigraphy varies between the traditions
in the different countries. In England and France micromorphological studies have been used (e.g., Corty
et al. 1989, Gebhardt 1997), for example in London (Corty et al. 1989), Worchester (Dalwood 1992)
and Paris (Cammas 1997). In Sweden there has been
no tradition of incorporating micromorphological
studies in archaeology so far. The exception is the
studies of soil profiles from cultivated terraces in the
counties of Halland and Närke and the occupational
strata of Birka (mentioned in Håkansson 1995 and
Håkansson 1997). Unfortunately, the results of those
studies have not been published thus far.
Measurements of various biological, chemical
and physical parameters are applied in geology in
order to make stratigraphical interpretations. Some
18
of this multiproxy approach has also been applied
to trace the possibly obscured stratigraphy of dark
earths. One approach has been to determine vertical
or horizontal compositional variations (Sidell 2000).
Chemical analysis and measurements of magnetic
susceptibility may also be useful when separating
dark earths formed in urban and rural environments
(Macphail et al. 2000). A clear indication of hidden
strata are the remnants of constructions found in situ
within the homogeneous stratigraphical unit, resting
on a former surface that now invisible in sections.
The stratigraphy of urban constructions
From an archaeological point of view, the most important components in urban occupational layers
are the physical remains of the town itself – its buildings, streets and yards. In the discussion concerning
what part of the occupational deposits are intentionally or unintentionally created (Järpe et al. 1979;
Andrén 1985, 1986), these constructions are considered intentionally created deposits (and may also be
referred to as ‘manifest’). It is important to realize
that medieval houses, and parts of houses, were often constructed during different time periods (e.g.,
Eriksdotter 1996) and that old structures rarely have
been left untouched by later activities. Therefore, a
building remnant may represent building phases that
span over several decades.
Parts of buildings preserved in urban strata generally consist of the lower units – the foundation,
which in turn may consist of fill, stones, sills, posts/
postholes and sometimes floor remains. Foundations
or parts of ovens and kilns are also sometimes preserved.
In archaeological studies, the focus is generally
placed on documenting the structural proportions
of house remains in order to interpret the type of
building and its function, and the spatial distribution between different buildings in order to locate
backyards, lanes and streets (Augustsson 1992).
In order to interpret building techniques, there has
been a focus on the parts that most clearly reveal
the upper structures of the building, for example
the arrangement and styles of sills and postholes (cf.
Goodburn 1995). The foundation layers of houses,
which generally are the remains that built up the occupational layers, have been studied in terms of their
general morphology. Only few, if any, studies have
until now focused on the material in those foundations, the fill that composes them. Since they often
contain reworked material, finds within the fills are
difficult to interpret and relate to time and place dependent contexts and are therefore considered as be-
Urbanised Nature in the Past
Figure 8: The collapse of a building controls the extension of debris layers deposited above the foundations. Examples
of collapses are: A) Outward collapse, B) Inward collapse and C) Collapse through tipping. Samples taken from building
debris (grey) may therefore be plotted as being outside the building, since constructions commonly are marked on excavation plans by the extension of their foundations (dotted lines).
ing of limited archaeological value (e.g., Roskhams
1992, 2001, Tagesson 2000a).
In some cases, the upper parts of buildings are preserved in the stratigraphy. This is especially evident
when buildings have been burned but sometimes also
deliberately demolished, generally in order to make
space for other constructions. These types of remains
are preserved as depositions of house debris consisting of fragments of the former houses and in some
cases, their content in the form of charcoal, wood,
fragmented bricks, chalk, mortar, glass, stones and
pieces of turf. Sometimes it is possible to identify layers of different composition within the house debris,
which may make it possible to understand which
materials composed the different units of the building.
When dealing with the stratigraphy of collapsed
constructions, it is important to consider how the
building came down (e.g., Keevill 1995, Robins
2003). Did the building collapse on its foundation,
or did it tip over in the process? If the building tipped
over, or if its walls fell outwards, the house debris
would also be distributed outside its foundations
(Fig. 8). The investigation of how a collapse of a
building took place may also reveal evidence of the
building techniques (Keevill 1995).
When new buildings were constructed in medie-
val towns, it was common to use debris from older
buildings as fill in the new foundations. Augustsson (1992) states that building materiasl in Swedish
towns were limited, which may be reflected in the
habit of recycling house debris as fill.
A special valuable type of stratigraphical remains
of destructed buildings is the traces of large city
fires, which often were well documented in historical records (Fig. 9). Residues of such fires may be
preserved as extensive and continuous charcoal horizons that contain building remains and objects affected by fire (melted glass, burned clay etc.). These
layers are often possible to identify even if they have
been truncated. If such identification is possible (and
supported by artefact typology) the dating of the
strata can be pinpointed, sometimes down to hours.
Also streets, lanes and yards may be preserved
within the stratigraphy, both as deposits and as horizons. When cobble streets and yards are preserved in
urban occupational layers, they generally consist of
a settling material (commonly sand) into which the
cobblestones are pressed. Sometimes the stones have
been removed and the settling horizon may then
be recognised by its surface morphology, with preserved imprints of the stones. At waterlogged sites,
wooden boardwalks are sometimes found. The most
common types of streets, lanes and yards in Scan-
19
J. Heimdahl
Figure 9: Fire could be extremely destructive among
densely built timber constructions and many Medieval and
Post Medieval towns were
burnt down at several occasions. Traces of large town
fires are sometimes preserved
stratigraphically and may be
used for dating.
dinavian towns were probably naked, tramped soil
without any paving at all. Remains of such surfaces
may be recognised by the compacted topsoil or the
tramping horizon. Old walking grounds may also be
recognised by the orientation of artefacts and other
objects that almost exclusively are deposited in horizontal positions.
Finds of former tramping grounds are generally
considered as being of high interpretative value. Objects found on those grounds may be considered as
primary deposits, and can therefore be connected
to a time and space dependent context (Tagesson
2000a).
Another type of urban construction is the largescale fill that was used to transform ground surfaces
within the town. Examples of this are the rearrangements or damming of rivers, filling and foundations of banks or shores, and filling in depressions
(Beronius-Jörpeland 1992). In order to transform
landforms or prepare an area for building, negative
forms such as pits, cavities, hollows and truncations
were also created (Yule 1992, Clark 2000, Tagesson
2000a). In geological terms the contact between the
truncated material and a later deposition is ‘erosive’
(indication of hiatus). In archaeological terms it is
sometimes called a ‘truncation horizon’.
The stratigraphy of waste
‘Waste’ would possibly be the most common answer
to the question of what mainly composes urban occupational layers, and probably many archaeologists
and geologists would agree on this point. There are
many reasons for this.
Waste may be considered a term for unwanted material. What is considered as ‘unwanted’ in a specific
situation is, of course, dependent on social conventions. Things that are ‘waste’ in one situation or in
20
a specific social context, may be considered valuable and useful in another. In Scandinavian medieval
towns, the things that were interpreted as waste can
be classified in different groups: by-products, broken
or used objects, and faeces – which also may be considered a type of by-product (Fig. 10).
For instance, by-products (or waste products) may
be wooden chips created during carpentry, bones
during the cutting of meat, or ash and charcoal from
hearths. This type of waste is the material that in one
way or another was originally brought into the town
from the surroundings. Another type of by-product
has its origin within the town itself, for example natural (or cultural) sediments that may be considered
as waste when being redistributed by digging. Besides by-products, broken, used or old products will
often also be considered waste. It is the waste of past
times, the small things forgotten, that in our times
will consist the absolute majority of the ‘artefacts’
studied by archaeologists (cf., Deetz 1996). A third
type of waste is faeces from humans and animals.
Cattle, horses, pigs, sheep, goats, dogs, cats and
fowls were kept on the streets during daytime. This
is the reason that dung constitutes a major part of
the organic compound in many urban occupational
layers. Faecal material from animals is often found
in urban refuse hips, which indicates that this material was removed from the streets. Human faeces
are generally found concentrated in latrines and on
dump piles where latrine buckets or chamber pots
were emptied.
There are many popular myths concerning waste
handling in Medieval and Post-Medieval times and
many have a mental picture of the medieval towns as
extremely dirty. Numerous authors have described
how household waste was dumped directly on the
street, which has contributed to the idea of the medieval town as a constantly growing waste pile – an
Urbanised Nature in the Past
idea that in turn has been used in order to explain
the presence of urban occupational deposits, since
they have been interpreted as the actual waste pile.
Archaeologists initially supported this picture since
it was impossible to find traces of cleaning and truncation, according to earlier excavation techniques
(Larsson 2000). During the latest decade this picture
has been adjusted. Partly because of the introduction of SCR, it has been possible to interpret patterns of refuse removal within urban environments.
Specific dumping places and dumping pits are often
identified, and an organised system of waste dispersal with wooden barrels seems to have been in use
in many towns. The systematic cleaning in Medieval
and Post-Medieval towns is also supported by written sources (Beronius-Jörpeland 2001).
Urban production of waste during the Medieval
and Post-Medieval times was limited compared to
later times and the recycling of material was probably common (cf. Drangert & Hallström 2002).
Organic by-products from cooking was used to feed
pigs, wooden waste was often used as fuel and when
things could not be recycled in other ways, they could
serve as fill in foundations for new constructions
(Beronius-Jörpeland 2001). In many towns there are
examples of how waste was used as fill in the construction of extensive land forming, for instance the
foundation of new waterfronts in Stockholm during
the 14th century (Hansson 1970, Dahlbäck 1982).
Urban pedogene soil processes
Alongside the depositional processes, like construction and waste handling, the urban environment and
its associated activities also led to the formation of
strata accorded to post-depositional process and
formation of horizons. The soil horizons formed in
urban sites can be developed by natural pedogene
processes that occur independently of the urban environment and also by processes directly linked to
the urban environment. Tramping by humans and
domesticated animals, grubbing of pigs and pecking of fowls cause culturally induced bioturbation in
the urban topsoil. At the same time horizons may
form by natural bioturbation, for instance caused
by roots, earthworms and other soil organisms. A
majority of the topsoil horizons in towns were probably truncated, but sometimes they were buried and
thereby preserved.
In the south Swedish lowland two orders of ‘natural’
pedogene soils dominate: Spodosoles (Sw: podsoler)
and a type of Entisoles (sometimes also referred to as
Inceptisoles), (Sw: brunjordar). The Entisols are developed in grasslands and broad leaf forests through
earthworm bioturbation (Fig. 11). Organic litter on
the ground is mixed with the upper part of the minerogenic material that constitutes the sub-soil. This
leads to the formation of A and B-horizons above
the unaffected C-horizon: The surface A-horizon is
characterised by humified organic matter mixed with
Figure 10: Deposition of waste occurs through different degrees of awareness. A) By-products, such as wood chip litter,
e.g. created through carpentry. They are unintentionally accumulated as litter on the floor or ground and later mixed with
the topsoil through post depositional tramping. B) Minerogenic waste created as a by-product from digging. They can
be left as unintentionally created waste piles, be dumped intentionally in waste piles or be reused as fill. C) Objects may
be dropped accidentally and are then considered waste by mistake. If new protecting layers do not cover the surface, the
objects dropped can be either tramped into the ground or cleaned away and deposited in waste pits or piles. D) Waste
from e.g. households was commonly and intentionally thrown in waste pits or given to pigs.
21
J. Heimdahl
Fig 11: Typical Entisol (Sw. brunjord), developed in Middle Swedish grassland. It consists of three horizons. The
A-horizon, a surface horizon of humified organic matter
mixed with minerogenic particles. The B-horizon, a subsurface minerogenic horizon enriched with organic matter.
The C-horizon, the unaffected minerogenic mother material.
minerogenic particles and the subsurface minerogenic B-horizon is characterised by the enrichment of
organic matter. If an area, for instance, a vacant lot
within a town is left untouched, it generally leads to
the establishment of ruderal plants and earthworms
begin to thrive. After some years this will develop
natural A and B-horizons. Such horizons (sometimes
partly truncated) are commonly found buried in archaeological sites and indicate old ground surfaces
that have been open, and relatively undisturbed, for
several years.
Human interaction with soil forming processes
is sometimes considered as ‘disturbance’ but soils
formed due to anthropogenic activity may also be
classified as its own order: Anthrosols (Gilbert 1989)
that may include soils affected by ploughing, digging, tramping, or chemical pollution. Individual
horizons within soils, affected by ploughing (often
rich in phosphate due to fertilizing) may also be
called ‘anthropic’ (e.g., Brady 1990). However, the
classification of Anthrosols is generally adapted to
modern soils (Gilbert 1989) and the letter system of
classifying different horizons within soils is not sufficient when classifying horizons in urban archaeological contexts. Instead the individual horizons are
referred to by the descriptions of the activity that created them such as: ‘tramping horizon’, ‘earthworm
horizon’, ‘root horizon’ or in combination such as
‘tramping horizon, affected by earthworms’.
22
The two major horizon-types formed due to cultural activities found in urban occupational deposits are tramping horizons (developed by humans
and animals) and cultivation horizons (developed
through ploughing and digging). Cultivation horizons, or cropmark horizons, are sometimes difficult
to separate from horizons developed through cattle
tramping. Their content and appearance in cross section may be similar. Both contain a mixture of cattle
faeces and minerogenic material, and both may be
developed to similar depths (c 10-20 cm). If studied
in detail in the field, they may be separated by different features in their contact with the unaffected
substratum, for example in cultivation horizons the
contact may be impressed by marks from ploughs or
shovels (e.g., Petersson 1999, Hedwall et al. 2000,
Karlenby 2002).
Ploughing is a very rough mechanical force that
generally destroys remnants of buildings and structures within the affected horizon, and archaeological interpretation in plough horizons is difficult, although possible (Alexander & Armit 1993, Sarnäs
2004). Tramping, on the other hand, may be gentler,
and the turbative force is not as large but still has an
effect on objects within the affected horizon. Experiments have proven that tramping effects by humans,
especially in sand, may cause dispersal effects on artefacts, not only on the horizontal plan but also in
their vertical displacement (Stockton 1973, Villa &
Courtin 1983). Another soil affecting process may
be heating of the ground, for example below hearths
or burned buildings (Corty et al. 1989). The effect of
earthworms is even smaller than tramping but still
these organisms can be capable of moving larger objects, such as bones and stones. The effects of earthworms on artefacts and archaeological sites have
been investigated several times (e.g., Armour-Chelu
& Andrews 1994; Grave & Kealhofer 1999; Lawson
et al. 2000; Davidson 2002).
Traces of earthworms may be found either by the
structural analysis of the soil, by macrofossil finds or
by worm tracks in the sediment. Earthworms’ faeces
are composed of mineral particles and humic material that stick together in aggregates. These aggregates form a structure called ‘crumb microstructure’.
Generally they are easy to identify with field observations but sometimes micromorphological studies
are required (Corty et al. 1989). A soil that contains
crumb microstructures obtains specific properties,
for instance it becomes much more resistant to erosion by rain and alluvial runoff (Brady 1990). The
cocoons formed on the worms’ clitellum constitute
the most common remains of earthworms (Fig 12).
They are easy to find and identify during macrofos-
Urbanised Nature in the Past
of water along the roots also leads to the transport
of oxygen. The rate of decomposition can fluctuate
through time due to changes in climate and local
environment, like nearby excavations. Excavations
lead to the drainage of surrounding strata, which
then increases decomposition rate. This in turn may
lead to the settling of the ground and the destruction
of buildings. The processes and effects of decomposition of occupational strata have been studied several
times (e.g., Borg 1993, Oxley 1993, Gardelin 2002,
Lagerlöf & Nord 2002, Wikström 2003).
4 Urban Plant Ecology
Figure 12: A) Earthworm cocoon formed on the clitellum (jointed segments at the anterior third of the body of
oligochaetes). B) Earthworm traces obscuring the contact
between two strata.
sil analysis, and may reveal the former presence of
earthworms even if a crumb microstructure has not
been identified. Tunnels burrowed by earthworms
are identifiable by characteristic tracks. They are
especially easy to identify when the worms have
moved from one strata into another since the material from the old strata will occur as tunnel fill in
the new strata (Fig. 12). If earthworms occur in and
between several strata separated by sharp contacts,
these contacts will gradually become obscured. This
makes it possible to exclude bioturbation by earthworms between strata whose contacts are sharp and
undisturbed.
Another important post-depositional effect is the
decomposition of organic material in the depositions. The decomposition occurs through activities
by microorganisms, mainly fungi and bacteria. This
activity is largely controlled by the access to oxygen,
which in turn is controlled by the amount of water
in the material. Decomposition activities are therefore low in waterlogged material. The presence of
water depends on the ground water table and the
capillarity of the material. Richness in organic material increases the fine-grained fraction through humus particles and the water is easily kept within the
strata. Preservation in coarse-grained material, like
gravel and stones, is generally poor if it is not situated below the groundwater surface. Preservation
along roots is generally poorer because the transport
From a perspective of botanical ecology, the urban
environment is a mosaic of ecological niches, providing habitats for a multitude of communities characterised by species with different strategies.
The urban environment has changed in many ways
since the Medieval and Post-Medieval times. One of
the most important changes is the urbanisation of
the rural economy. The end of animal husbandry
within towns and the disappearance of horse driven
transport have decreased the content of nutrients in
the systems. The transport of seeds and fruits from
meadow and pasture plants by animal faeces and
field weeds from crops has almost ceased. Streets and
yards are almost exclusively covered with asphalt or
stones and few cultivation plots for kitchen plants
remain. On the other hand, cultivation for esthetical
or recreational purposes has increased since the mid
19th century when public parks were introduced (c.f.,
Nolin 1999). In those parks, plant communities of
cultivated species and weeds co-exist.
There are also examples of urban environments
that remain relatively unchanged. Past and present
processes of soil exposure are probably similar.
Loosely packed and exposed soil provides a niche for
r-strategists (cf., Hitchmough et al. 2001) – pioneer
plants adapted to quick environmental fluctuations
by a rapid reproductive capacity and the capacity to
form seed banks (Begon et al. 1996, Crawley 1997).
Plants that are resistant to mechanical disturbances,
such as tramping, find their niches in both past and
present towns on paths and between cobblestones
on streets and yards. It is also common to find refugias of natural environments in towns (Gilbert 1989,
Botkin & Beveridge 1997). Along cliffs and water
lines, it is also common to find a flora dominated
by K-strategists – competitive plants with long life
cycles.
Present urban environments are often characterised by a large number of exotic plants introduced
both intentionally and unintentionally (Gilbert
23
J. Heimdahl
1989). Gardens and parks are especially rich in
foreign plants, and it happens that imported plants
naturalise in vacant ecological niches or take over
niches by interspecies competition. Unintentionally
introduced plants commonly spread in harbours and
places where cargo is unloaded, for instance on market places. The high introduction rate of neophytes
provides a stress to the urban ecology in general (Gilbert 1989) and it has been observed that many alien
species become a part of the urban seed bank (Kostel-Hughes et al. 1998).
The introduction pattern of alien taxa has changed
since the Medieval and Post-Medieval times. Both
intentional introduction of cultural plants and unintentional introduction have increased in the last
centuries (Lundqvist 2000). Proportionally, the intentional introduction has increased much more
than the unintentional introduction because of the
large quantities of cultural plants. Although the early
towns were probably rich in neophytes and past urban environments should also be suitable to study
from this perspective (cf., Preston et al. 2004, Wittig
2004).
Urban fossil floras commonly consist of a mixture
of plants derived from different environments (see
Chapter 5). This mixture may be analysed through
the ecological grouping of those species that can provide important information about both local and regional environments (Latalowa et al. 2003).
Earlier studies of urban archaeobotany in Sweden
and neighbouring countries
The material in this study has been compared with
the results from other investigations of urban Medieval sites in Sweden, and also from Finland, Norway
and Denmark where archaeobotanical methods have
been applied (Fig. 13). Some results are unpublished
or exist as reports from local museums or university departments. In other nearby countries, such as
Germany, Poland and Great Britain, urban biostratigraphical records have been more frequently studied
and published than in Scandinavia. Examples are the
investigations in Cracow (Wasylikowa 1978), Göttingen (Hellwig 1995), Kiel (Wiethold 1995), Lednicki (Polcyn 1995), York (Kenward & Hall 1995),
Wroclaw (Kosina 1995), Dublin (Geraghty 1996),
London (Giorgi 1997), and Elbag and Kołobrzeg
(Latalova et al. 1998, 2003).
Most archaeobotanical studies in Sweden have focused on prehistorical sites but there are some examples of the studies of plant remains from Medieval
and Post-Medieval urban sites. Urban archaeobotanical work has been performed on plant material
24
from 11th – 13th century Lund, 12th-14th century Uppsala (Hjelmqvist 1963, 1991, Regnell in Carelli &
Lenntorp 1994, Regnell in Carelli 1995, Påhlsson
1983, 1991a, 1991b) and 16th century Gävle (Elfwendahl & Påhlsson 1991). During the archaeological excavations at Helgeandsholmen in Stockholm,
there was a close collaboration between the National
Heritage Board (RAÄ) and the Geological Survey of
Sweden (SGU). Palaeoecological reconstructions,
based on diatom and pollen floras, were performed
by Miller and Robertsson (1982) and the plant macrofossils were studied by Griffin (1983) and Berggren (1984). In Stockholm, studies have also been
carried out on the material from the Post-Medieval
area of ‘Kvasten’ (Heimdahl 1999b) and from the
park ‘Humlegården’ (Hansson & Dyhlén-Täckman
1999). Urban archaeobotanical studies in Göteborg
have been performed at four Post-Medieval sites
(Larsson 1985, 1986). Geoarchaeological studies
in a wider sense have been carried out around and
in the Viking Age town of Birka (Miller & Clarke
1997 and Risberg et. al 2002), including archaeobotanical analysis (Hansson 1995, 1996, Hansson &
Dickson 1997, Heimdahl 1999a). Birka, however,
differs from other Swedish urban contexts since the
occupational deposits are not waterlogged and the
preservation of organic remains is poor. Much of the
study has therefore focused on the clay-gyttja deposited offshore, just outside the town. This is similar
to the sediments of the former lake Fatburssjön,
that represent depositions from the Bronze Age to
the 19th century (Robertsson et al. 1995). In addition, earlier analyses of plant macrofossils of samples from the 16th -17th century have been performed
in Norrköping (Ranheden 1999). Macrofossils were
also sampled in the castle of the Medieval town of
Vadstena (Ranheden in Hedvall et al. 2000). Macro
remains from the Medieval town of Sigtuna (9th-13th
century) were studied by Engelmark (2002).
Urban palaeoenvironmental reconstructions in
Finland have been undertaken in the Helsinki area
using different biostratigraphical methods (Vuorela
& Lempiäinen 1993). In Turku macrofossil analyses
were carried out by Aalto (1994) and Lempiäinen
(1985, 1988, 1994 &1995). During the reconstruction of the environmental history of Turku, a combination of palaeoecological methods (pollen, diatoms
and plant-macrofossils) was used (Vuorela et al.
1996). The Finnish data is probably well suited for
comparison with the Swedish sites since Finland was
strongly influenced by Sweden during the Medieval
and Post-Medieval times as it was under Swedish administration during AD1323-1809.
Extensive geoarchaeological and palaeoecological
Urbanised Nature in the Past
13
Sweden
Norway
60
Finland
14
12
11
1
2
3 4
15
Estonia
16
5
6
7
Denmark
10
55
9
8
10
Baltic Sea
20
Figure 13: Location of urban sites, which has been archaeobotanically investigated, and are here compared with the results of this thesis.
5. Norrköping
1. Uppsala
Griffin et al. (1988)
Ranheden (1999)
Påhlsson (1983, 1991a, 1991b)
Viklund (2000)
12. Bergen
6. Vadstena
Krzywinski et al. (1983)
Ranheden in Hedvall et al. (2000)
2. Sigtuna
Krzywinski & Kaland (1983)
7. Göteborg
Engelmark (2002)
Hjelle (2002)
Larsson (1985, 1986)
3. Birka
13. Trondheim
8. Lund
Hansson (1995, 1996)
Griffin & Sandvik (1989)
Hjelmqvist (1963, 1991)
Miller & Clarke (1997)
Sandvik (1992, 1995)
Regnell in Carelli & Lenntorp (1994)
Hansson & Dickson (1997)
Regnell in Carelli (1995)
Heimdahl (1999a)
14. Turku
Risberg et al. (2002)
Lempiäinen (1985, 1988, 1994, 1995)
9. Copenhagen
Vuorela et al. (1996)
Moltsen (2002)
4. Stockholm
Aalto (1994)
Miller & Robertsson (1982)
10. Svendborg
Griffin (1983)
15. Helsinki
Jensen (1979)
Vuorela & Lempiäinen (1993)
Berggren (1984).
Robertsson et al. (1995)
11. Oslo
16. Tartu
Hansson & Dyhlén-Täckman (1999)
Griffin (1979)
Heimdahl (1999b)
Sillasoo (2002)
work has been carried out in urban medieval contexts in Norway, for example in Bergen (Krzywinski
et al. 1983, Krzywinski & Kaland 1983). Investigations specifically focusing on plant macrofossil anal-
ysis have been made in Oslo (Griffin 1979, Griffin et
al. 1988) and Trondheim (Griffin & Sandvik 1989,
Sandvik 1992, 1995).
Denmark has a long tradition of archaeobotanical
25
J. Heimdahl
Figure 14: Examples of the regional
origin of plant diaspores recorded in
an urban environment.
investigations of Medieval contexts. However, during
the Medieval Time Denmark was heavily influenced
by northern continental Europe, and the Medieval
Danish archaeobotanical material is more comparable to the German or Polish than to the Scandinavian material. Results from Svendborg (Jensen 1979),
København (Moltsen 1999, 2002) and a summary
of plant macrofossil data from the Medieval Danish
sites (Karg and Robinson 2002) were used as northern European case studies in this investigation.
5 Taphonomy of urban macro remains
The study in this thesis is largely built on the analysis of plant macrofossils. In order to understand a
fossil record, both palaeoecological and taphonomic
aspects must be considered. Taphonomy of urban
material is especially complex, and it is therefore
necessary to include it as a background for palaeoecological analyses and interpretation of results.
Taphonomy includes all factors, both natural and
cultural, that affect the final setting of a fossil record,
including post-depositional processes as well as the
sampling and treatment of material in the laboratory.
This account will mainly focus on the plant macrofossil material – seeds, fruits and other diaspores. A
more extensive taphonomic account of pollen grains
can be found in Vuorela (1999). I have chosen to
divide the taphonomic factors into seven groups:
biology; deposition; human influence; preservation;
reworking; sampling, preparation and registration;
and personal bias.
26
1. Biology
Life strategies of plant species vary. K-strategists
have a long and less effective reproductive cycle than
r-strategists (e.g., Begon et al. 1996, Crawley 1997).
K-strategists more commonly form wood tissue and
have thicker roots. Differences in seed dispersal and
seed production (Howe & Westley 1997) will influence the fossil record. Some plants are dioicic (separated sexes of the individuals) and only female, fruit
setting plants will be registered through seed or fruit
identification. Plants of the same species may act differently from time to time depending on environmental factors. They may produce different amounts of
seeds or set fruits in different periods, and thus give
signals of varying magnitude in the fossil record.
Since plant macrofossil analysis commonly deals
with diaspores (as they are relative to other plant tissue that are both resistant and easier to determine to
species), we will come across plants that have been
going through seed setting. This also means that
male individuals (in the case of dioic plants) will not
be found in this fossil record. It is also important to
take into account that seed and fruit production varies between different plant species in quantity, season
and frequency.
2. Depositional processes and ecology in urban environments
Depositional processes within the urban environment
are complex (Fig. 14 and 15) (cf. Thomas 1997). In
this discussion, the fossil plant record has been di-
Urbanised Nature in the Past
vided into four groups, based on taphonomic origin
of the plants: A: the local flora; B: the regional flora;
C: plants from pastures and meadows, and D: cultural plants. These groups can in turn be subdivided
as discussed below.
A: The local flora
The local flora is considered to include plants, which
have grown in the immediate vicinity of the investigated area. The Medieval and Post-Medieval urban environment was characterised by continued
spatial rearrangement of buildings and structures,
and by the large production and deposition of waste
and nutrients. Soils were exposed and covered by
new depositions rapidly, both by human activities
and large-scale domestic animal bioturbation (e.g.,
pigs). In this type of environment, alluvial and colluvial processes lead to the exposure of soils. These
environmental factors will disturb plant communities, and small-scale migration of plants will occur
between patches in the area. The in situ urban flora
with ruderal plants and weeds has pioneer strategies
with a high capacity of dispersal and low competition ability, according to trade-off effects (e.g., Crawley 1997). This means that these plants often have a
rich production of seeds and can form seed-banks
or seeds that are easily dispersed (Rees 1997, Howe
& Westley 1997). The Medieval urban flora generally developed different biotopes directly connected
to the soil types within the site (Gilbert 1989). These
biotopes can be divided into eight groups (Fig. 15):
Figure 15: Local urban flora environments (1-8) and transport of material and seeds within the town (A-I).
1. Tramping resistant flora on streets and in yards
2. Loose soil flora
3. Nitrophilous flora
4. Turf roof flora
5. Refugal flora on cliffs, etc.
6. Harbour flora, neophytes etc.
7. Weeds in local cultivation plots
8. Flora thriving along walls, etc.
A. Seed dispersal through footwear and wheels
B. Import of (sometimes exotic) seeds
C. Storing and processing of seeds before marketing
D. Export of seeds
E. Cleaning of streets and yards, dumping of waste
F. Cleaning of dung from streets and yards, used as fertilizer
G. Dung from stables
H. Stored and processed crops
I. Processed cereals used within the town or exported
27
J. Heimdahl
1. Tramping resistant communities occurring on
pathways, backyards and in streets.
separated if their occurrence is connected to other
species that are specific to certain local or regional
environments.
2. Loose soil communities growing on loosely packed
debris and soil stacks.
C: Plants from pastures and meadows
3. Nitrophilous communities found near latrines,
waste piles, dung heaps and along house walls and
ditches, where moisture and nutrients are concentrated in the soil.
4. Turf-roof communities will occur if roofs are overgrown with e.g., grass or plants selected for fire protection (Krzywinski et al. 1983).
5. Remains of the pre-urban natural flora may occur
as refugium biotopes, for example river and seashore
flora, or plants growing on cliffs or rocks.
6. Harbours where cargo is handled may act as a first
environment for neophytes. Floras in harbours and
wharves often contain specific species.
7. Weeds and kitchen plants may grow on cultivation
plots within the town. Cultivation within and just
outside towns is documented in historical sources.
8. The ground adjacent to walls may act as a substrate for weeds. The environmental factors along
walls vary according to geographical position, house
type, street-type etc.
B: The regional flora
In this study the regional flora is defined as all ruderal and natural plants occurring outside the excavated area, both outside and in the town. The regional flora is mainly represented by plants along
roads and in the nearby town blocks. These plants
can be spread by wind or by attachment to animals,
humans (Clifford 1956) or wheels (Millberg 1991).
Seeds transported in this way are, however, difficult
to differentiate from seeds grown in situ, since they
are often derived from identical biotopes. Sometimes
they may also arrive from different environments,
such as forests and wetlands.
Many plant species thriving in urban areas can
also grow as weeds in cultivated fields. Among the
finds from Norrköping and Karlstad, there are also
plants that are common in many different environments and thus are hard to correlate to any specific
habitat. This is especially relevant for the Chenopodium album-type and also the species Cirsium arvense, Fumaria officinalis, Galeopsis tetrahit/G. bifida,
Lithospermum arvense, Solanum dulcamara and
Stellaria media. These plants could have been growing in fields, along roads and pathways, in the town
or locally within the investigated area. They may be
28
Grazing by cattle can lead to a concentration of plant
remains from pastures and meadows in urban areas
by deposition of faeces and hay. This taphonomic
factor plays a major role in most Medieval and PostMedieval urban sites. Cattle sometimes also graze
ruderal plants and weeds, and some of the ruderal
plants are abundant in pastures as well. If isolated
coprolites (in this case, faeces that are distinguished
as coming from one individual) are found, it may be
possible to determine the species of the animal that
produced it by the morphology or species-specific
parasites. Plant macrofossils in coprolites can also
provide important information on the grazed area,
or during which season the grazing or cutting of the
hay occurred (Moe 1996, Moltsen 1999, Karlsson
2000).
D: Cultural plants
Cultural plants are referred here as plants that are
known to have been regularly used by humans. They
could have been collected from a wild or cultivated
population and might have been brought into the
town for trade, storage and/or processing. If a cultural plant is represented, both in the pollen flora
and by macrofossils, it may be an indication of regional cultivation. This is not always the case since
pollen grains can also be brought into the town in an
artificial way (cf., Faegri and Iversen 1989).
Cultural plants are generally processed in specific
ways which may affect the fossil record. For example, harvested cereal crops are processed through
different methods of threshing, sieving and cleaning.
Fossil records of crops may differ according to which
steps have been taken in their handling. (cf., Hansson
1997, Viklund 1998, Hambro Mikkelsen 2003).
3. Human influence
Humans can selectively have affected plant communities due to cultural habits that may be unknown
to us. Some species may have been cleaned away or
favoured for different reasons, for example due to
unpleasant characteristics (like stinging or burning
tissues), pleasant characteristics (like beauty), or due
to mythical ideas (like luck or misfortune). Smallscale cultivation or the collecting of species, according to religion, tradition, medicine and decoration,
Urbanised Nature in the Past
must also be considered (cf., Johnson 1999).
the biotopes for plant remains found in this type of
deposit must be handled with care.
4. Preservation of plant macrofossils
Macrofossils are preserved by water logging and occasionally by carbonisation through heating. Different preservation processes of the same original plant
community will lead to different fossil records. Water logging generally leads to a wider and more complete spectra of preserved plant remains but there are
exceptions. Cereal grains and wild grasses are more
easily preserved by carbonisation, while fruits of e.g.,
the Apiaceae family are much better preserved by
water logging (Gustafsson 2000). Another example
is the differences between r- and K-strategists. Since
r-strategists often have the capacity to form seed
banks, the seeds tend to be bigger and more hardcoated than seeds from K-strategists. This may lead
to that seeds from r-strategists are over represented
in materials with bad preservation status.
At Norrköping and Karlstad, about 95% of the
counted macrofossils were preserved as un-carbonised specimen, since the embedding medium consisted
of a dense, fine-grained deposit with high capillarity
and low permeability. Only 5% of the material consisted of carbonised diaspores, concentrated mostly
on the old surfaces in connection with fireplaces or
debris from burnt houses. Samples with carbonised
material were generally lacking un-carbonised material and vice versa but in some cases they occurred
together. This may indicate different taphonomic
origin of the plant material and the two groups were
interpreted separately.
5. The reworking processes
The reworking of deposits in urban environments
is usually extensive. It may affect the preservation
status of the fossil content by mechanical, biological and chemical deterioration. This can lead to the
relative concentration of hard macrofossils in the redeposited material, (given that they also occur during the reworking process or are present in the mixed
material). This also makes robust macrofossils less
suitable to use for reconstructions since they can
be reworked many times and still remain well preserved. For the same reason, we can put more trust
in fragile material.
Some samples from ‘Konstantinopel’ were characterised by high concentrations of plant macrofossils
with the same size as the medium sand fraction (0.20.6 mm). This occurred in well-sorted, water deposited alluvial material, dominated by silt and is probably an effect of sorting by water. Conclusions about
6. Sampling, preparation and registration
Additional taphonomic factors occur by sampling,
storing, processing and finally by analysing the fossil content of the samples. For example, the flotation process is a method that works differently
with different sedimentological mediums, and it is
a good idea not to handle all samples in the same
way (Wright 2005). During wet sieving, the choice
of sieve size will have an effect on the composition
of the retrieved material, which in turn may affect
ecological interpretation (e.g., Birks 2001; Zohar &
Belmaker 2005). During analysis, it is also important
to have a clear classification and quantification strategy for fragmented material, and for the comparison of the different anatomical features preserved as
plant macrofossils. How do we compare leaves with
seeds?
7. Personal biases
The final taphonomic factor is connected to the person performing the analysis. It is therefore important
to ask the question: what are my personal biases?
It appeared to me that I first observed certain types
of fossils. These were usually the most common
types of moderate size (1-2 mm) like Chenopodiumtypes, Carex sp. and Urtica sp. This was probably
due to their high abundance within the samples and
that they were easily noted with the magnification
used (c. ×8-15). But it also may have been a kind
of “favouring the expected”. To avoid this, the samples were analysed on a number of occasions to ensure that the more unusual or discrete fossils (e.g.,
Poaceae-fruits) were identified as well as the more
common remains.
The trade-off of favouring the expected is to favour
the unexpected. This seemed to happen when I made
unusual or exotic findings. This then led to attempts
to find more fossils of the same type, which perhaps
made me ignorant to the more common findings.
Again, to go through the samples repeatedly was my
strategy to avoid this bias.
6 Study sites
Norrköping (Paper I, II, IV, V)
Norrköping is situated along the river Motala Ström,
between Lake Glan in the west and a bay of the Baltic Sea, Bråviken, in the east (Fig. 16). The excavated
29
J. Heimdahl
Figure 16: A) Map over Norrköping. The investigated area is marked with black in the upper left corner of the marked
block. The present river Motala ström is shown in dark grey, and the light-shaded area marks the former extension of the
stream before the rearrangements after AD 1640. B) Simplified map of Quaternary deposits in the area (After Bergström
and Kornfeldt 1973). Till and bedrock are marked with triangles, glaciofluvium with dots, fine grained marine sediments
with white, and light grey marks the alluvial deposits of the river (dark grey).
site is located in the centre of the town (Fig. 16).
The bedrock consists of migmatised granites,
gneisses and mica schists (Bergström & Kornfält
1973) and is partly exposed in the highland area
southwest of the town. In the east, thicker Quaternary deposits cover the bedrock. About one kilometre south of Norrköping, the deposits are generally
dominated by different littoral sediments (Fig. 16).
The eastern lowland is characterised by flat areas
with post-glacial clay and silt underlain by varved
glacial clay and silt and southwest of the town, the
landscape is hummocky and consists of till and bedrock outcrops. An esker runs straight through the
town from northwest to southeast. The investigated
site is situated where the river Motala Ström cuts the
esker. The glaciofluvial deposits are surrounded by
coarse silt and till. The slope within the excavated
area is part of the river valley of Motala Ström, and
the esker itself does not seem to affect the local topography (cf., Lindgren-Hertz 1999). Downstream,
the riversides are dominated by alluvial deposits,
from clays to coarse silt rich in organic material. The
distribution of this alluvium is poorly known, especially the area along the southern riverside, where
the investigated area is situated (Bergström & Kornfält 1973).
The investigation area is situated close to a bay
of the Baltic and thus the shore displacement must
be considered. Present land uplift in the area is 3.0
mm/yr and according to a relevant shore displacement curve (Persson 1979), the rate has probably not
changed significantly during the last 3000 yrs. The
altitude of the shoreline of the Baltic Sea during the
30
13th century can be estimated to be about 2.4 m a.s.l.
The present surface of the excavation site is located
about 9 m above present sea level and the substratum of the oldest occupation layers is situated about
7 m a.s.l. Since the Medieval times, the site has not
been affected by the regressive sea level. The elevation of the earliest medieval ground surface in the
excavated area was about 4.5 m a.s.l.
The flat landscape is suitable for cultivation. Humans have been present in the area since the land
in the vicinity started to rise above sea level about
2000 years ago. The river Motala Ström, which in
this part is characterised by rapids and turbulent water, made the place attractive for salmon fishing and
ideal for establishing mills and therefore, it became a
place of economic interest (Ljung 1965).
Norrköping was first mentioned as a trade centre
in 1283, but it was not given its town privileges until
1384. Written sources indicate that during the Medieval times, Norrköping was an important centre
for trade and administration, where both the state
and the church had interests (Lindeblad 1997). During the middle of the 16th century, as a result of the
reformation under the regiment of Gustavus Vasa,
Norrköping became the most important Swedish
harbour for the export of iron. The town expanded
rapidly and during the 17th century, due to industrialisation, Norrköping became the second largest
town in Sweden, next to Stockholm.
The Medieval constructions in Norrköping have
so far remained unknown because of the major reconstructions of the city plan during the 16th and
17th centuries, including a major reconstruction and
Urbanised Nature in the Past
filling of the river Motala Ström, which was made
narrower and deeper (Fig. 16). Therefore, the oldest
remains normally found during archaeological excavations are from the 16th century or later (Parr 1987,
Kjellén 1996, Hållans et al. 1999).
In the excavated area the preserved occupation layers are sloping towards the west and the former river
course, which according to the rectified map of 1640
was very close, perhaps only some meters away from
the border of the present investigation area (Fig. 1).
Due to the sloping substratum, the layers are thicker
and better preserved towards the west. The occupation layers disappear about 50 meters upwards from
the western edge of the excavated area (LindgrenHertz 1998).
Karlstad (Paper II and III)
Karlstad is situated in southwestern Sweden on the
river Klarälven delta that fills out a bay on the northern shore of lake Vänern (Fig. 17). The lake was
isolated from the sea due to land uplift c. 7000 BC
(Fredén 1988). Karlstad is the only town in Scandinavia that is located on an active river delta. Hummocky terrain with exposed and sparsely till-covered
bedrock surrounds and partly penetrates the delta
plain.
Between 7000 and c. 2500-2000 BC the shoreline
of Lake Vänern retreated ca 20 km southwards due
to land uplift (Sandegren 1939, Heijkenskiöld 1981,
Sundborg & Heikenskiöld 1972 and Fredén 2000)
and the delta sedimentation moved southwards to
the present area. During the last 2000, years the
shoreline of Lake Vänern has remained more or less
stable and local changes are mainly due to a continuous built up of the delta. Coring in the delta revealed
silty and sandy sediments with a depth between 10
and 20 m (Fredén 2000). The present water level
of Lake Vänern is 44.0 m a.s.l. and the water level
fluctuates about ±1.3m between low and high water (Heikenskiöld 1981). Heikenskiöld (1981) estimates that the delta situated at the excavation area
was built up over the sea level about 700 BC to AD
1. During the beginning of the Roman Iron age, a
sandbank dividing the river into two branches was
formed. Later the delta mainly grew in the eastern
and western branches of the river. By AD 700 the
central part of the delta had the same characteristic
features as today. From the 13th century the expansion of the delta shifted to the south, and since then
the central parts of the delta have remained stable,
although certain morphological changes of the spit
of Sandgrund was seen during the 19th century.
The hills around the flat delta plain display several Iron Age and Medieval settlements. There seems
to have existed a Medieval trade centre located at
a place called ‘Tingvalla’. In AD 1290 Tingvalla is
mentioned as the centre where markets and juridical
processes were held (Nygren 1934), but the exact location and nature of Tingvalla is not known, and no
archaeological evidence has so far been found. However, single artefacts from the Middle Ages found
within Karlstad indicate nearby activities during this
period (Andersson & Schedin 2001).
Karlstad was founded as a strategic iron-shipping
town between the mining areas in middle Sweden
Figure 17: A) Map of central Karlstad. The investigated area is marked with black on the left side of the marked block.
The river Klarälven is shown in dark grey. The line that surrounds and lies southeast of the church marks the hill ‘Lagberget’. A part of the hill ‘Marieberg’ is marked in the southwestern corner. B) Simplified map of Quaternary deposits in the
area (after Fredén 2000). The alluvial delta material is light grey, and the river Klarälven and Lake Vänern are dark grey.
White areas are dominated by till and bedrock but also include fine-grained sediments and peat accumulations.
31
J. Heimdahl
(Bergslagen) and the Swedish west coast. Karlstad
was given its town privileges in AD 1584 by King
Karl IX and until now, no urban structures pre-dating that year has been found (Lundh et al. 1994,
Ängeby 1995). The town had its main economical
growth during the 18th and 19th centuries.
The accumulation of sand seems to have been
a problem in Karlstad for a long time and regular
dredging of the river was necessary for the shipping.
Flooding in the town centre also occurred regularly,
except for the hilly areas of till-covered bedrock that
are seen above the flat delta plain (Andersson &
Schedin 2001).
The excavated area is located on the flat delta area
in the town centre between the till-covered hills of
Lagberget in the northeast and Marieberg in the
southwest (Fig. 17). The c. 1 m thick occupational
layers were deposited directly on, and partly developed as horizons in the flat delta surface and they are
evenly distributed over the investigated area.
7
Methods
Field methods and sampling strategies of this project
are described in more detail in Paper I. Because of
the nature of the urban stratigraphy, continuous
sampling was not undertaken in all stratigraphical
units. The main method used was plant macrofossil analysis, which was suitable to describe the local
environment as well as human activities. The macrofossil content was diagnosed in all stratigraphical
units excavated. In remains directly related to human activities, e.g., house debris, the method was
limited to the search for indicators of past vegetation
and cultural plant use. In these contexts, sampling
in each stratigraphical unit became more extensive
in order to adapt to the archaeological excavation
strategy.
Other biostratigraphical methods used were pollen and diatom analysis. These methods were only
applied when more specific questions arose. Pollen
analysis was used as a complement to plant macrofossil analysis on the oldest strata because of the
lack of cereal grains in these layers. In order to trace
the origin of the deposits, diatom analysis was used
where the stratigraphy presumably was influenced
by alluvial action. Some stratigraphical units were
studied more carefully for sedimentological features
and in these cases, samples were taken for texture
analysis and the determination of organic carbon
content. Fabric analysis was carried out when it was
difficult to distinguish between dumped filling masses and till.
32
Field work
Since the geological fieldwork was carried out during
the archaeological excavations it had to be adapted to
the archaeological framework (Menander & Karlsson 2002, Heimdahl et al. 2003; Paper I). At each
site the archaeological excavation was performed according to SCR methodology and the stratigraphy
was plotted in a Harris Matrix. The positions of all
stratigraphical units, as well as artefacts and samples,
were documented three-dimensionally in a database
and visualised in the GIS-program Arc View.
A sampling technique for macrofossil analysis was
developed and adapted to the single context methodology used at the excavation (Paper I). Pilot sampling was performed in each layer except those that
were unfavourable for the preservation of organic remains, for instance deposits including coarse gravel
or stones. The samples aimed for macrofossil analyses were collected in cardboard boxes with a plastic
inner film. The samples were normally floatated and
wet-sieved immediately after sampling, according to
the method described by Wasylikowa (1986). The
enriched remains were investigated under a dissecting microscope at the site and the plant macrofossil content was qualitatively diagnosed in order to
evaluate the need of additional sampling before the
layer was totally excavated. After this pilot analysis,
the samples were stored in water filled plastic containers.
Stratigraphical cross sections were described and
drawn both by the archaeologists and the author. The
colour of the strata was classified according to the
Munsell Soil Colour Cart (Munsell Colour 2000). In
some cases the drawings were dissimilar because of
differences in the interpretation of the stratigraphy.
In layers where sedimentological structures could be
of interest for sampling, metal boxes were pressed
into the wall and cut out so that sufficient parts of
the strata were preserved intact. The filled boxes
were subsequently wrapped in plastic and stored in a
cold room before sub-sampling.
In order to minimise contamination by recent vegetation, a survey was made of the seed-producing
plants in the present local urban flora. The composition of the modern local flora was also compared
with the fossil urban flora investigated. Investigations were carried out on five occasions during each
excavation in an area up to 10 metres away from
the excavation site. Plants with seeds spread by wind
were documented with extra care, even if they were
growing a long distance from the excavation site e.g.,
Betula spp. and Salix spp. The time of seed setting
was noted and plants that were about to set fruits
close to the site were, if possible, removed.
Urbanised Nature in the Past
Macrofossil analysis
Pollen analysis
In order to facilitate an ecological interpretation of
the macrofossil content, between 300-500 diaspores
were identified to species level in each sample investigated. Other plant remains which could be identified, such as needles, leaves and bark, were registered
but not included in the percentage calculations. The
macrofossil samples were, when necessary, wetsieved for a second time and cleaned in the laboratory according to methods described by Wasylikowa
(1986).
After the wet sieving the samples were examined
as subsamples of c. 3-5 ml at a time. The microscope
used in the laboratory had a magnification of ×8-100.
The samples were first described according to their
general composition of tissues and biota. The groups
used were wood, charcoal, bark, herbacea epigaeic
(stems and leaves), herbacea hypogaeic (roots), insects, statoblasts (hibernate-capsules of bryozoans),
puparia (pups, eggs, cocoons etc. of lower animals),
Ichtyes (bones and scales from fish), Mammalia
(bones and hair from mammals) and artefacts, e.g.,
slag, glass fragments and brick fragments were also
included in this description. The amounts of the most
frequent components: wood, charcoal and bark was
roughly quantified as ‘1’ (single objects), ‘2’ (<5%
of the visual field) or ‘3’ (>5%). The diaspores were
counted as single units.
Fragmented material was noted as parts of units
if the original parts could be reconstructed or the
amounts were roughly quantified into separate units.
Fragments of a seed taxon, represented by a single
element from the original carpum (e.g., a hilum),
could be counted as one unit but in contrast, fragments without these special elements were not considered for quantification.
The remains with characteristic cell patterns, such
as Poaceae and Juncus fruits, were determined under
a light-microscope with higher magnifications (×1001000). For specimens where identification was of
extra importance, further analyses were undertaken
with a SEM-microscope (Paper II).
The identification of the seeds was mainly carried
out by consulting a reference collection and the works
of Korsmo (1926); Bertsch (1941); Körber-Grohne
(1964, 1991); Katz et al. (1965); Berggren (1969,
1981); Beijerink (1976); Tallantire (1976); Jacomet
(1987); Schoch et al. (1988); Jacomet et al. (1989);
Blidow and Krause (1990); Anderberg (1994) and
Krause (1997). After identification, the seeds were
stored in distilled H2O in 5ml plastic containers. A
mixture of glycerine, ethanol and thymol was used
for storing very fragile material.
Pollen analysis was undertaken to investigate the cereal pollen content in the dark earths of Norrköping.
Samples designated for pollen analysis were sub-sampled from the sediment collected in the metal boxes.
In order to concentrate pollen and spores from the
sediment, a standard acetolysis method was used
(Erdtman 1936; Berglund & Ralska-Jasiewiczowa
1989). A collection of reference slides and the work
of Moore et al. (1991) were used for identification.
The cereal type pollen grains were measured and surface structures were studied according to Beug and
Firbas (1961) and Andersen (1979).
Diatom analysis
Analysis of diatom composition were undertaken in
order to investigate ecological signals of terrestrial
or aquatic environments. Samples for diatom analysis were sub-sampled from the metal boxes. Siliceous
microfossils were extracted according to the method
described by Battarbee (1986). Identification of the
diatoms and the interpretation of the ecological conditions were made with the use of Kramer and LangeBertalot (1986; 1988; 1991a; 1991b) and Round et
al. (1990). The diatoms were grouped according to
their habitat, either as terrestrial or aquatic. Only
one of the six samples contained significant amounts
of diatoms for a quantitative analysis.
Grain size distribution
Texture analysis was performed as a complementary stratigraphical tool in order to reveal obscured
stratigraphical changes and in order to trace possible
mother material for fills. When sediment is reworked
(for example by digging), its structural features will
disappear and changes but the texture will remain
intact (cf., Paper I). Samples for grain size distribution were taken directly from the open transects and
on surfaces where stratigraphical units had been exposed. Texture analyses were performed on gravel
and sand particles by dry sieving using sieves with
square-formed holes. The silt and clay fractions were
determined by hydrometer analysis (Kompendium i
jordartsanalys 1995).
Organic carbon and loss on ignition
The analysis of organic carbon content and the loss
on ignition (LOI) was performed in order to reveal
obscured stratigraphy of the dark earths. It was determined on the dark earths from both Norrköping
and Karlstad. Continuous samples, each 1 cm thick
33
J. Heimdahl
yielding c. 1-2 cm3, were extracted from the dark
earth at 3-5 cm intervals. Organic carbon content
was determined by a carbon sulphur detector (ELTRA CS 500). The LOI was calculated as percentages from the weight loss of dried samples, which
were slowly heated to +550ºC and kept at that temperature for two hours (Kompendium i jordartsanalys 1995).
C-Dating
14
Seven plant macrofossil samples (five from Norrköping and two from Karlstad) were AMS dated at
the Ångström Laboratory, Uppsala University. The
material used was sub-sampled from the macrofossil samples (Table 1), which were stored in distilled
H2O in a cold room at +4ºC, between the summer
of 2000 and the autumn of 2001. Fragile seeds from
terrestrial plants found in a primary position (e.g.,
floors, tramping horizons and hearths) were chosen
for dating to minimize the risk of using reworked
material. The seeds were gently cleaned in distilled
H2O and detritus was washed away with a small nylon brush under a dissecting microscope. This material was first slowly heated at +70ºC for 2h and then
dried at +105ºC for 8h and placed in small glass jars
with plastic screw lids.
Other dating methods
Dendrochronology and the typology of artefacts and
coins were also used for dating purposes. Thomas
Bartholin at the National Museum in Copenhagen
carried out the dendrochronological work. The archaeologists at the excavation undertook the typological datings. Monica Golabiewski Lannby at the
Royal Coin Cabinet in Stockholm performed the
identification of coins.
Ecological grouping
The identified plants were grouped according to
ecology using the systems described by Grime et al.
(1988), Ellenberg et al. (1991) and Mossberg et al.
(1992, 2003). The system of Ellenberg et al. is based
on Central European data, and groups the plants according to their different requirements (e.g., light,
moisture, nutrients and temperature) expressed in
numbers. The system is hierarchic and a plant can
only be described as thriving either in light or shadow. This compilation covers about 90% of the species found in Norrköping and Karlstad. Grime et al.
(1988) describe the biotopes of plants in the British
Isles according to where the plants are found and
34
evaluate their degree of abundance with a number
(a scale from 1-5). The system is heterarcic, which
means that a plant may occur with the same frequency in different habitats. In this way plants with generalist strategies can be separated from plants with
special strategies according to their habitat. This system covers about 60% of the plant species found in
the investigations. Mossberg et al. (1992, 2003) is
a comprehensive flora with descriptions of the ecology and habitats of plants found in the Scandinavian
Peninsula. This was mainly used for plants that were
not included in the systems of Grime et al. (1988) or
Ellenberg et al. (1991) Mossberg et al. (1992, 2003)
was also useful for comparing descriptions of plant
ecology in order to check if there are differences between the regions.
The following publications were also used for
information on single plant species: Jensen (1985,
1998); Kroll (1995, 1996, 1997, 1998, 1999, 2000);
Schultze-Motel (1992, 1993, 1994); Johnson (1999)
and Mabberley (2000).
Biological nomenclature
The Latin names of plant species and taxas are according to the continuously updated species list published on the internet by the Museum of Natural
History in Stockholm. The version used here was
updated 2004-01-19 (Karlson 2004). The English
names are according to Qualtrocchi (2000).
8 Summary of Papers
Paper I
Jens Heimdahl, Hanna Menander and Pär Karlsson,
In press 2005: A New Method for Urban Geoarchaeological Excavation, Example from Norrköping,
Sweden. Norwegian Archaeological Review. In press
November 2005.
During excavations of complex urban occupational
deposits in Norrköping, new procedures were elaborated in order to combine archaeological, geological
and archaeobotanical fieldwork. This fieldwork was
also based on parallel work by members of the different disciplines throughout the whole excavation.
The archaeological fieldwork was based on SCR. In
order to understand the archaeological fieldwork
procedures and the basis of interpretation, the geologist (Jens Heimdahl) also spent time excavating
with the archaeologists.
The elaborated procedures resulted in continuous pilot sampling and on site preparation and di-
Urbanised Nature in the Past
agnostics of samples. When excavation of a new
stratigraphical unit started, it was sampled by the
geologist who immediately enriched and analysed
the material under a dissecting microscope at the
site. Hence, a pilot survey of the macroscopic content of the stratigraphical unit was available before
it had been fully excavated. The pilot surveys facilitated the field interpretation of the strata. On several occasions the results revealed the functions of
constructions, and provided environmental glimpses
already in the field. For example, it was possible to
take additional pilot samples in order to investigate
if the macrofossil content within the strata differed
spatially, and a comparison to other strata could
also quickly be performed. The method also made
the correlation easier between strata cut by younger
truncations. The pilot surveys were also used to trace
former root-horizons. Such horizons were analysed
to determine which type of plants that had grown
on the site, information that in turn could give clues
for how long time surfaces had been left open and
untouched.
All strata were geologically studied according to
sedimentological structure and texture, parallel to
the archaeological stratigraphical interpretations.
These double interpretations resulted in constantly
ongoing field discussions. On some occasions the different interpretations confirmed each other, in others
they opposed each other. The discussions that followed proved important for the development of a
mutual understanding and in some cases led to new,
sometimes surprising conclusions.
The geological interpretations revealed that the
thick minerogenic strata, located below the dark
earths, were fills consisting of reworked glaciofluvium and littoral sand. Without the geological expertise
present, they would probably have been interpreted
as the natural substratum. The geological field interpretations also revealed new ways to critically treat
stratigraphical units as information sources. This
especially counted for material that traditionally is
considered reworked, like fill. By analysing the fill
texture and comparing it with the texture in other
local material of natural origin, it was on some occasions possible to determine the source material for
the fill. Another way of dealing with the problem of
reworking was to look at the degree of fragmentation of fragile organic macro compounds. Finds of
large pieces of leafs or fragile seeds may be used to
exclude reworking.
Geological field interpretation also resulted in the
discovery that the occupational deposits to a large
extent were of alluvial origin. Many of those alluvial deposits consisted of silt lenses that apparently
had accumulated in water ponds. Some of the water
ponds had acted as traps for material from surrounding ground surfaces. Surfaces are important for archaeological interpretation, and since many surfaces
had disappeared though truncations or were located
outside the excavation area, the macro content of
water pond sediments could sometimes be used to
reveal cultural activities and environment on those
surfaces.
Paper II
Jens Heimdahl, 2005: Urban Sediments as Indicators
of Changes in Land use and Building Tradition in
two Swedish Towns, AD 1200-1800. (Manuscript)
Results and conclusions from sedimentological studies of occupational deposits at the excavations in
Norrköping and Karlstad were compared in order to
reconstruct urban environmental development and
site formation processes.
The site in Norrköping is situated on a slope towards the river Motala ström, and the occupational
layers were deposited as slope front fill on a substratum of littoral and alluvial sand. The occupational
deposits were 3-4 meters thick downslope and disappeared 10-15 m upslope from the excavation limit.
The lowest 1m thick layers consisted of minerogenic
sediments, probably of littoral and glaciofluvial origin, dumped partly in the flooded stream during the
13th century. On top of these fill, two dark earth
units with obscured strata developed during the 13th
to 14th century. Wooden boardwalks were built on
top of the uppermost dark earth during the mid 14th
century. Above the boardwalks the stratigraphy is
characterised by c. 1 m well-stratified urban occupational deposits originating from 1400-1660.
The occupational layers at the site in Karlstad are
deposited on top of the active delta of river Klarälven. The substratum consists of the top set beds of
the delta. The oldest culturally affected deposits at
the site is the uppermost delta sand in which a 3040 cm thick dark earth with obscured strata have
formed, probably during the 16th century, but it may
also contain older units. This dark earth is overlain
by 1 m well stratified urban occupational layers deposited between c. 1600-1800 and at some places,
interlayered by delta beds from flooding events.
The dark earths at Norrköping and Karlstad seem
to have developed in similar ways. They consist of
85-95% of minerogenic material with the identical
texture as the unaffected substratum. The organic
component seems to be dominated by cattle faeces.
Sedimentological structures indicate that this dung
35
J. Heimdahl
was tramped into the ground, possibly during wet
conditions. There are also several structures revealing
that the homogeneous dark earths contain obscured
strata. The dark earths are believed to have formed
during a combination of repeated alluvial sedimentation and a continuous tramping of cattle, thus successively deepening the horizon and homogenising
the individual alluvial deposits. In Karlstad the alluvial deposits originate from regular flood events on
the active delta. In Norrköping they are formed by
alluvial runoff on the slope. This also explains why
the dark earths here are thicker downslope.
The alluvial deposits in Norrköping continued to
form during the formation of the well-stratified urban occupational deposits. Silty alluvium accumulated repeatedly in the depressions of the town, mainly
in streets and lanes between the houses, and on some
occasions, created negative casts of the urban landscape. When alluvial silt filled the streets, new constructions had to be elevated in order to avoid moisture. This habit is thought to have formed a cycle of
human response to natural effects thereby inducing
each other and resulting in the growth of urban occupational deposits.
At both Norrköping and Karlstad fills used in the
foundations for houses were investigated with grain
size analyses. The results show that the fill used in
the early stages of the urban development was local
material of a fine fraction, not suitable for foundations. In the foundations built later, the material was
coarser and taken from more distant deposits. This
shift is thought to represent a professionalisation
of building construction. In Norrköping it seems to
have occurred during the beginning of the 17th century. In Karlstad the shift occurs later, during the 18th
century.
Paper III
Jens Heimdahl, 2005: Botanical Evidence of Changes
in Vegetation and Cultural Landscape in Post-Medieval Karlstad, Sweden. (Manuscript)
Macrofossil evidences from Karlstad reveal glimpses
of environmental development of the urban and regional area, cultivation, trade, and differences between grazed pastures and mowed meadows.
The oldest 14C-dated samples taken in the delta
sediments had calibrated ages of 215 (±40) BC and
AD 165 (±40). A dense forest vegetation represented by birch and alder formed on the newly built up
delta surface. Light demanding plants, for example
Prunus spinosa, Rubus idaeus and Bidens tripartite,
thrived along channel banks, and different Juncus
36
and Carex species were growing at the waterline.
Submerged plants like Nitella opaca, Isoëtes echinospora and Potamogeton spp. probably grew in the
delta channels.
Cattle grazing and the creation of meadows deforested the delta during the time when the black earth
was formed, sometime between AD 500 and 1500.
An increase of ruderal plants in the uppermost part
of the undisturbed delta sediments provides an indication of human occupation predating the formation
of the dark earth. The macrofossil concentration in
the dark earth is heterogeneous and varies both spatially and vertically. The composition of the flora,
however, is homogeneous, and is heavily dominated
(up to 90%) by Juncus spp., mainly Juncus bufonius
and other wet meadow plants like Carex spp. The
taphonomy of wet meadow plants is interpreted as
cattle faeces. Samples taken from fresh cattle faeces
at a nearby wet meadow with ungrazed Juncus tufts
reveal that the faecal material becomes heavily dominated by Juncus fruits, due to the grazing of fruits
stuck to the surrounding grazed vegetation.
The macrofossil record in the urban occupational
deposits is dominated by a species composition that
also characterises cattle faeces. This confirms the historical notes from the 16-17th centuries that the town
was largely composed of farms. Hay remains were
found stuck to the inside of a compressed bucket
that was situated on the floor in a burnt down small
stable from the early 17th century. The macrofossil
composition of the hay, dominated by Filipendula ulmaria and Poa palustris, differs completely from the
composition in the cattle faeces, dominated by Juncus bufonius, found on the stable floor (that seems
to have been covered by spruce branches). This show
that the cattle kept in this stable had been grazing
and was not fed with hay mowed from meadows.
Since hay was likely used as winter fodder, this indicates that the stable was not used for winter stabling.
An explanation to this may be that it was used specifically for cattle that were to be slaughtered.
The urban cultural layers were also rich in the remains of cultivated, collected and imported plants.
The finds of cereal grains were dominated by Avena
sativa (oat). According to historical sources, this was
the most frequently cultivated plant in the county of
Värmland at this time, which indicates that locally
cultivated crops dominated the urban use of cereals. Macrofossil finds also indicate the cultivation of
Fragaria moschata (Hatbois strawberry) during 1718th century, Rubus subg. Rubus sect. Rubus (blackberries), Pisum sativum var. arvense (field peas) and
Fagopyrum esculentum (buckwheat). Further, there
is botanical evidence of cultivation of Nicotiana rus-
Urbanised Nature in the Past
tica (wild tobacco). This cultivation is historically
documented to have been introduced in Karlstad by
Gustav Claren during the mid 18th century. Historical documentation and find positions in the debris
of a burnt house may contribute to a dating of the
destruction of the building to June 8, 1752, when
there was a large fire in Karlstad.
The discovery of a fruit from Pimenta officinalis
(allspice) in a stratum from the latter part of the 17th
century indicates the importation of exotic species.
Allspice has earlier only been archaeologically found
twice, in England and Poland, and this is probably
the oldest find in Europe so far. There is also other
evidence of long distance trade in the form of rare
species specifically known to grow at docking places
and in harbours, for example Erucastrum gallicum
and Chenopodium murale/ C. vulvaria.
Paper IV
Jens Heimdahl, 2005: Botanical Evidence of Environmental and Traditional Changes in Norrköping,
Sweden, AD 1200-1660 (Manuscript)
During excavations in Medieval and Post-Medieval
Norrköping, macrofossil and pollen evidences revealed local and regional floral changes, cultivation
of plants, preparation of food and importation of
exotic plants.
The oldest macrofossils were found in alluvial deposits underlying the oldest occupational deposit – a
fill from c. AD 1200. The composition indicates that
the slope towards the river Motala ström partly contained a wet meadow with tufts of Juncus sp. and
Urtica dioica, and partly a drier sand bank vegetation with for example, Arenaria serpyllifolia, Potentilla argentaea and Arabidopsis thaliana.
The urban phase at the site seems to have started
with the dumping of filling masses on the slope towards the river. On these filling masses, a dark earth
developed through cattle tramping between AD
1200-1400. Nitrophilous plants with pioneer strategies like Thlaspi arvense and Lamium album besides species thriving on faeces like Urtica dioica and
Chenopodium glaucum/rubrum seem to have dominated the site together with plants resistant to tramping, for instance Polygonum aviculare and Plantago
major. This combination of plants indicates a rural
environment with dung heaps, tramped paths and
plants growing along fences and buildings.
Above the dark earths, complex strata of urban occupational layers were deposited between AD 1400
and 1660. The composition in the layers indicate a
shift in the local plant ecology since earlier common
plants like Plantago major and Lamium album disappear and are replaced by newcomers like Aethusa
cynapium and an increase of Hyoscyamus niger.
Centaurea cyanus, Rumex acetosella and Spergularia arvensis are examples of plants interpreted as
regional field weeds. Field weeds especially common
in fields with autumn sawed rye, for example Bromus secalinus and Agrostemma githago, was found.
The cattle that were brought into town were probably mainly grazing on wet meadows with different
species of Carex spp.
Secale cereale (rye) dominates among the cereals in
the pollen record from the dark earths (1200-1400)
and in the cereal macrofossil composition between
1400 and 1550. If this reflects local cultivation, it
is partly in line with historical evidences since the
area became part of the so called ‘rye belt’ during
the 15th century. Of special interest is a burnt find of
what is interpreted as threshed remains from a harvested rye crop from 1400-1550. The cereal grains
are here mixed with seeds from typical field weeds
like Centaurea cyanus and Rumex acetocella but the
most common non-cereal plants are Poa palustris
and Trifolium hybridum, which are typical meadow
plants common in mowed hay. This may be either a
mixture of a crop and hay, or possibly a crop from a
field that previously was used as a meadow.
Among the most commonly found cultivated
plants were hops (Humulus lupulus), well known to
have been used for the flavouring of beer. Beer making seems to have been common at the site between
the 14th and 16th centuries. In some samples, hops
were found together with Myrica gale, which was the
most commonly used beer flavour in Sweden before
hops was introduced. The finds also indicate that a
mixture of H. lupulus and M. gale was used for beer
flavouring in 1400-1550. Filipendula ulmaria was
over-represented in the samples that contained other
beer flavours. This plant is earlier known to have
been used as a flavouring of mead during the Viking
Age. The find in Norrköping may indicate that this
tradition survived into the late Middle Ages.
Further, seeds from imported plants like grapes
and figs were found. An early find of grape, probably
deriving from the 14th century, indicates the presence
of a clerical, or upper class, community.
Paper V
Jens Heimdahl, 2005: Archaeobotanical Evidence of
Early Tobacco Cultivation in Norrköping, Sweden
(Manuscript)
Botanical evidence of tobacco cultivation was found
37
J. Heimdahl
during the investigations in Norrköping. It is the first
archaeological find of tobacco in Sweden. Light microscope and SEM analysis resulted in the identification of the seeds as Nicotiana rustica (wild tobacco)
and Nicotiana spp. (tobacco unspec.) Since finds of
fossil tobacco seeds are rare, the seeds are carefully
described. No leaf tissue from tobacco was found in
the samples containing the seeds. In total, 42 seeds
were identified. Although a 14C-date indicates a
younger age, artefacts and stratigraphical information suggests that cultivation occurred sometime
during 1560-1660 – possibly the earliest tobacco
cultivation in Sweden.
The conclusion that the seeds indicate cultivation
in Norrköping is based on several facts. Tobacco for
smoking or sniffing was imported as leaves. In order
to maximise the size of cultivated tobacco leafs, the
flower buds were cut off the plants. The possibility
that the seeds derive from imported tobacco leaves is
therefore minimal.
So far the oldest known cultivation of tobacco in
Sweden took place in the garden of Uppsala castle in
1632. During the 17th century, tobacco cultivation
in Sweden was not aimed for large-scale production
but for medical use. Tobacco was considered a panacea – a miracle medicine able to cure many types
of diseases. Early tobacco cultivation for medical or
scientific use is a probable explanation to the find in
Norrköping. From written sources, tobacco cultivation for industrial use is known to have occurred in
this town between 1720 and 1930.
9 Discussion
Urban strata, a formation model
From a geological perspective, it is natural to define urban strata as two different types of phenomenon: sediments and soil horizons, meaning strata
formed by depositional and post-depositional processes respectively. This classification has earlier been
stressed in archaeological contexts by both geologists
(Limbrey 1975, Lundqvist 1986, Corty et al. 1989,
Carter 1992), and archaeologists (Beronius-Jörpeland 1992). A third important factor that affects site
formation are the negative effects from truncations,
erosion (Tagesson 2000a) and decomposition. The
processes that controlled the formation of the urban
stratigraphy in Norrköping and Karlstad can be divided into three major groups: Depositional, Postdepositional and Truncation/erosion/decomposition
processes.
Deposition provides the material, which is redistributed and reworked during post-deposition, and
the third process, truncation/erosion, removes the
material. Truncation/erosion may be also followed
by redeposition. Again, each of these groups may
contain both natural and cultural elements. One of
the major questions archaeologists ask about site
formation is which of the units were formed by intentional acts, and which were formed unintentionally (Järpe et al. 1979, Andrén1986, Beronius-Jörpeland 1992, Larsson 2000). The answer influences
the information potential of each stratum. Moving
towards a classification of possible site formation
causes as being either intentional or unintentional, I
would like to add natural processes as a third factor.
Table 2 presents how the tree groups of processes,
depositional, post-depositional and truncational/
erosional, combined with the tree groups of causes,
intentional, unintentional and natural, may result in
different types of stratigraphic features.
A compilation of processes that affects the formation of urban occupational strata can be combined
into a model (Fig. 18). This model combines the geological and archaeological approaches to the stratigraphy. The model is divided in three main steps: causes, cultural actions/natural events and stratigraphic
Table 2: Classification of urban occupational strata
Natural
Alluvial (water)
Depositions
Colluvial (gravity)
Eolian (wind)
Horizons
Earthworm horizons
Root horizons
Erosion/truncation/de-
Alluvial erosion
composition
Microbiological decomposition
38
Unintentional
Cattle droppings
Unintentional waste
Tramping horizons (humans and cattle)
Live stock turbation
Tramping erosion
Intentional
Constructions
Fills
Waste and dump
Plough horizons
Cultivation horizons
Truncations
Urbanised Nature in the Past
Cause
Stratigraphic result
Action/event
Organic
g
Waste and dumps
enin
id d
/m
g
in
ts
Fills and fundaments
amen
mp
und
f
Du
f
o
n
tion
atio
Building debris/remains
estruc
Cre
on/d
i
t
c
ru
t
s
n
Co
Cattle faeces
n
tio
c
tru
Alluvial
es
ng
pi
l
Deposition may be
fal
Deposition
ain
post-depositionally
r
or
affected (reworking on
d
Post-deposition
small scale)
oo
Di
gg
in g
/p l
Depth scale in meters
o ug
hin
g
1
0,001
0,01
0,1
Fl
Culture
Dr
op
D
Strata formation
Intentional
Minerogenic
Mixed
Unintentional
Tramping horizons
stock
Live stock turbation horizons
orms
of earthw
ence
s
e
r
P
plants
Growing of
oo
M
ic r
do
ob
iol
io
r ra
og
infa
ic a
Root horizons
n
Truncations
ll
Erosion
l ac
tivity
Preservation and disappearence
of strata may affect natural and
cultural conditions
Decomposition
Disappearence
of strata
Erosive
contacts
Preservation
of strata
Strata destruction
at
nc
ru
g/t
gin
Dig
ng
lki
wa
g.
Fl
Earth worms horizons
Deposition and horizons
may disappear or be
reworked by truncation
or erosion
E.
Natural
Reworking
g
ng of live
rking
Nature
H oldi
Plough/crop horizons
Rewo
Tramp
in
Strata
(Layers and horizons)
Figure18: Model for the formation of occupational strata within a site. Disappearance of material from this model will
result in depositions on other sites. The system is influenced by the opposite situation.
results. The stratigraphic results are in turn divided
into: strata formation (depositional and post-depositional) and strata destruction (including truncation/
erosion/decomposition) effects. The model illustrates
how cultural and natural causes contribute to site
formation in both the depositional and the postdepositional phase, and also how the stratigraphic
results in turn can act as a trigger mechanism for
cultural and natural responses (cf., the cyclic model
in Paper II).
All types of processes that bring material to the
site are here referred to as depositional. From a geological perspective, they can be considered as ‘sedimentological’ processes. The depositional processes
result in accumulations of different layers. The intentional deposits dominate the occupational layers
in both Norrköping and Karlstad. The main volume
of the deposits consists of minerogenic layers that
were transported to the site with specific intentions,
mostly to reshape the local landscape, for example
to make a terrace on a slope, as in Norrköping, or
to construct elevated foundations for buildings. For
39
J. Heimdahl
these purposes mainly minerogenic material was
used. Reworked house debris are also intentional
deposits. The destruction of houses may have been
unintentional but often the material of destructed
houses was truncated and used as fills in new foundations, and the unintentionally created debris is thereby intentionally reworked (cf., Tagesson 2000a). A
special type of intentionally deposited material was
sand that was spread on icy grounds during wintertime. This sand was deposited with a purpose but
when the snow melted in the spring, it became redistributed by alluvial processes and by cleaning. Waste
piles, dung heaps and latrines are examples of intentionally created organic deposits but all traces of organic waste piles found in Norrköping and Karlstad
contained 40-80% minerogenic material. The fact
that cattle faeces were dumped within the town and
not brought to the surrounding fields indicates an
overproduction, which is also confirmed by written
sources (see Paper V).
The second most common depositional factor in
Norrköping and Karlstad was natural events (Paper
II). The major natural process was alluvial and resulted in the sedimentation of silt and sand in water
ponds formed in depressions. In Norrköping there is
also an example of small mudflows. Regularly occurring exposure of sandy material in the slope results
in erosion during rainfall and snow melt. The alluvial slope runoff in Norrköping probably worked as
a trigger mechanism for a certain cultural responses.
The concentration of alluvial and mudflow deposits
to depressions results in drainage problems in these
areas, which led to that buildings had to be elevated
by their foundations in order to avoid the moisture,
which in turn created new depressions in the streets.
Hence, this includes a nature-culture cycle of reactions and responses (cf. Paper II). This is probably
one of the reasons why occupational deposits are
thicker in depressions. The cycle was inhibited when
the foundation materials became coarser, with better
permeability and more resistance to alluvial erosion.
(In Fig. 18 the bottom arrow that leads from the
strata and the erosive cintacts back to the cultural
and natural causes represent these processes.) A fully
natural process dominates the alluvial material in
Karlstad – the regular flooding of the river Klarälven
and the formation of top set beds on the still active
delta.
Examples of unintentional deposits are dropped
objects and animal faeces dropped on the ground
in the streets and yards. Normally, material deposited on the ground was mixed into the topsoil by
post-depositional processes such as tramping and
bioturbation by earthworms. To find these types of
40
deposits unaffected by post-depositional processes is
extremely rare.
Tramping by humans and animals was probably
the most important of the post-depositional processes that occurred in the Medieval and Post-Medieval
urban environment. Experiments have proved this
process to be able to redistribute objects up to 17 cm
in depth (Villa & Cortuin 1983) in sandy material
during just one day of tramping. However, with the
exception of dark earths, tramping horizons on the
sites in this study are 3-10 cm deep. Cobblestones,
wooden boardwalks and a compact humic ground
inhibited the tramping effect.
Natural soil formation processes occurred parallel
to the tramping. There are several examples of strata
in both Norrköping and Karlstad where earthworm
traces were present. This is indicated both by horizons with crumb microstructure and macroscopic
finds of earthworm cocoons. It was quite common
to find traces of root horizons together with traces
of earthworms. Traces of smaller soil-penetrating
organisms like nematodes and Oribateids were also
found in many samples.
Examples of intentionally created post-depositional processes are ploughing or digging in order
to prepare a soil for cultivation. Soils of this type
were not found at any of the sites although a 16th
century plough-horizon had earlier been identified in
Karlstad, c. 200 m east of the present site (Lund et
al. 1994).
The macrofossil record from Karlstad indicates
that the development of soil horizons occurred during summer and autumn (cf. Paper III). Due to frozen
ground no organic material was mixed into the soils
during wintertime. Cattle faeces loaded with fodder
plants remnants from mowed meadows (winter signal) are absent in the urban soils and must therefore
have been deposited during the grazing season. Since
deposition of winter droppings loaded with fodder
plants most likely occurred, their absence implies
that the droppings were cleaned from the streets before the thawing of the ground. It could have occurred during snow ploughing but since snow is not
always present, their absence also implies that the
frozen streets were cleaned from dung also when they
were snow-free – probably due to a regular habit of
cleaning the streets. This is in line with the idea that
an organised cleaning occurred in the towns during
the Medieval and Post-Medieval times (cf., BeroniusJörpeland 2001).
Intentional truncation and unintentional/natural erosion created negative features found in Norrköping and Karlstad. These features are revealed by
erosive contacts between layers. Truncations may be
Urbanised Nature in the Past
Figure 19: Formation of dark earth through continuous land use (in this case, cattle handling causing tramping horizon)
and repeated alluvial events causing deposition of alluvial sand. The stratigraphy is repeatedly obscured by the tramping
but may also be preserved, e.g. by root horizons from vegetation and by postholes from constructions.
during snow ploughing. Natural erosion may occur,
for example through alluvial processes. In this study
erosion has been harder to recognise than truncation, as it occurs on a smaller scale. On the other
hand, the material that is eroded and redeposited by
alluvial process has been easier to identify.
The formation of dark earth
s
rie
es
tu
ad
C
en
ec
D
Ye
a
rs
s
th
on
M
ks
The dark earths of Norrköping and Karlstad were
formed by a combination of depositions by natural
events through alluvial processes and the post-depositional unintentional formation of soil horizons by
W
ee
s
ay
H
D
ou
rs
es
ut
in
M
Se
co
nd
s
recognised by their regular extension that excludes
natural or unintentional processes. When a truncation has cut one or several strata, it is sometimes possible to identify and trace the eroded or truncated
material that is redeposited as fills nearby. This is possible when the redeposited material contains a mixture that is possible to identify, for instance through
recognisable specific pieces or lumps. It is possible to
make these observations in the field, although soil
micromorphology provides a more powerful tool
when dealing with these features (cf., Carter 1993).
Erosion by unintentional acts may be, for example
hollowed walking paths or streets that are eroded
Faecal dropp
Deposits
Fills
Alluvial deposits
Waste/dump/middening piles
Fire debris
Accumulation of charred material in kilns and on cooking places
Accumulation of litter on floors
Plowing/cultivation horizons
Tramping horizons
Horizons
Root horizons
Earth worm horizons
Fig. 20: Duration of urban strata formation. Note that deposits generally have a longer duration than horizons.
41
J. Heimdahl
cattle tramping (Fig. 19).
The post-depositional processes led to the formation of soil horizons in the exposed ground surfaces.
When cattle were present at the site, new organic
material in the form of dung was deposited on top
of the sand. The mixture of sand and dung occurred
by cattle tramping but probably also by other pedogene soil forming processes, such as bioturbation by
earthworms and roots. In this way a tramping horizon mainly composed of a dung-and-sand mixture
was formed. However, alluvial processes continued
to affect the area, and additional sand and silt were
deposited on top of the horizon. Since the cattle handling at the site continued, the deposition and mixing of the dung into the tramping horizon also continued. The horizon affected the ground all the way
below the contact between the old ground surface
and the newly deposited alluvial sand, and erased
this contact. This process continued and the result
was dark earths that contained several obscured beds
of alluvial material and several overlapping obscured
tramping horizons (Fig. 19).
The obscured stratigraphy of the dark earths in
Norrköping and Karlstad was revealed through the
traces within them, such as preserved fragments of
minerogenic units, traces of constructions that apparently were built on top of obscured surfaces and
the varying organic compound and macrofossil content that differed through depth (Paper II, cf., Sidell
2000).
The reason why the dark earths at the investigated
sites ceased to form was probably due to the change
in land use when the area was divided into plots in
order to raise houses. Even if cattle were still kept
within the towns, movements of the animals were
restricted to streets and backyards that were partly
paved, inhibiting alluvial effects. Tramping horizons
of cattle do occur also in the strata above the dark
earths but were not developed to the same depth or
complexity.
Sediments, soil horizons and culture
The formation of deposits in the urban environment
generally occurred during short-term intervals while
post-depositional formation of soil horizons normally had a longer duration (Fig. 20). Fills in foundations and terraces were most likely formed during minutes, hours or days. Waste deposits may, as
a whole unit, have a longer duration of months or
years but parts of the waste heaps can be formed
during seconds. Geologically speaking, the urban
occupational deposits are extremely rich in hiatuses since no continuous accumulation takes place.
42
The effective depositional time of the urban layers
in Norrköping and Karlstad may be a few days or
weeks in total, even though the whole stratigraphy
represents a development during several millennia.
The pedogene post-depositional soil formation process had a longer duration. The tramping horizons developed in some of the deposits represent units that
were formed through ‘the unintentional activities of
the daily life’. If the total formation time of these
soil horizons are added to the total formation time
of the deposits, the result is more likely to represent
decades instead of days or weeks but it is still important to remember that we are trying to reconstruct
millennia from the fragments of those decades.
Harris’ (1979) statement that a stratigraphic sequence comprises depositions and interfaces is, in
my opinion, too generalized. Larsson (2000) may
be sociological correct when he states that “the
surface is the scene upon which the social interactions occurred” but it may also be stratigraphically
misleading. The idea that the surfaces are the most
interesting stratigraphical units to the archaeologist
(Gardelin et al. 1997, Larsson 2000) may lead to
some confusion when trying to understand how the
ground was affected by activities. Surfaces are twodimensional and constantly changing on a substrate
and if they are buried, they are extremely difficult
to trace through excavation. Surfaces themselves are
rarely preserved in a stratigraphy because of truncation and erosion. In fact, most of the contacts/interfaces between the urban deposits of Norrköping and
Karlstad are erosive. Instead the traces after those
‘activity surfaces’ have to be searched for in the soil
horizons developed as three-dimensional strata in
the deposits that constituted the ground at a specific
period. The social interaction mainly took place during the post-depositional phase, and it is therefore
the post-depositional features – the tramping horizons etc. – that must be studied in order to interpret
this daily life activity, and thus the cultural and social
complexes.
Still, it has also been proven fruitful to trace social
and cultural changes by studying the deposits. Alluvial beds may contain reworked objects from lost
surfaces and objects found in minerogenic deposits
with known origin may be considered as primary
deposited (Paper I). In addition, textural studies of
fill have proven rewarding. The shift from locally
used material in the fills to material with ‘exotic’
and coarser texture probably reflects a professionalisation of the building tradition (Paper II). Among
urban historians such a change has long been known
but it has not been known when it occurred, or if
it developed at different times in different towns,
Urbanised Nature in the Past
and in different blocks within the town (Augustsson
1992). The investigations in Norrköping and Karlstad suggest that this shift occurred at different times
in different towns, but it is not known if it occurred
simultaneously in all areas within the these towns.
This professionalisation may also have inhibited
the further formation of well-stratified urban occupational strata. The use of coarser material led to
better drainage and higher resistance to erosion by
alluvial processes. This change also resulted in more
advanced drainage systems and the paving of streets
and backyards become more common. The paving
inhibited soil formation by tramping, and the streets
became easier to keep clean (cf., Beronius-Jörpeland
2001). It is probably not a coincidence that well
stratified urban strata are not found after the reorganisation of building tradition was introduced. The
younger urban occupational deposits are coarser,
water logging is inhibited and the preservation status of organic material in this material is therefore
poor.
Larsson (2000) stated that we might expect a decrease of natural (geological) processes within the
urban environment in comparison to a rural environment. The results in this thesis speak in favour of
the opposite: The specific urban environmental conditions at Norrköping seem to have enforced geological processes. In Karlstad, the geological, alluvial
processes were not affected at all until the control of
the river in the beginning of the 20th century. It is also
worth mentioning that urban occupational deposits
generally are thicker than rural occupational deposits. The comparisons I have made between excavations indicate rather that naturally formed geological deposits are more commonly found interlayered
within urban deposits than rural deposits. This also
suggests that the urbanisation in Medieval and PostMedieval towns, with their constant ongoing soil exposure, reworking and land use shifts, increased the
activity of local geological processes.
10 Conclusions
• Stratigraphic interpretations are more complete
and reliable when archaeologists and geologists carry out excavations together. Possibilities of continuous field discussions enhance the prospects of mutual understanding between the disciplines. Methods
connected to Single Context Recording are fully
adaptable to a continuous geological fieldwork during archaeological excavation.
• Continuous pilot diagnoses of macro contents in
samples during excavation greatly contribute to field
interpretations, concerning both interpretation of
stratigraphy, functions of structures and past local
environments.
• The presence of a geologist during archaeological
excavations contributes with knowledge concerning
both natural and cultural factors connected to the
site formation processes. Naturally formed sediments
may be studied to obtain cultural information, for
example alluvial sediments may have acted as traps
for material on truncated surfaces or areas situated
outside the excavation area.
• There is evidence of small changes in the local
urban flora through time, probably as an effect of
interspecies competition. Marked floral changes occurred according to changes in land use. In Karlstad
there is evidence of a neophyte harbour flora with
rare species, nowadays limited to sporadic occurrences on the west coast. Many species are found
which probably had a more northerly distribution
during the 14th –19th centuries than today.
• Botanical evidence combined with historical data
suggests that the main consumption of cereals in the
towns derived from local crops. Rye dominated in
Norrköping and oat dominated in Karlstad. In Norrköping evidence of a transition between a grass-clover meadow and a rye field was found. There are
also indications of cultivation of berries, for example
Fragaria moschata in Karlstad during the 17th and
18th centuries. In Karlstad and Norrköping evidence
of tobacco cultivation was found. In Norrköping
tobacco cultivation occurred between 1560-1660,
and may be one of the earliest tobacco cultivations
in Sweden. In Karlstad it occurred during the 18th
century, and by historical sources it is possible to
connect to Gustav Clareen’s cultivation of tobacco
1741-1772.
• Comparison between the content of plant macrofossils in mowed hay and cattle dung in Karlstad
strongly suggests the use of a specific stable as a
slaughterhouse, not used for winter stabling. The
floral composition of meadows and pastures differed and there existed several types of meadows
that were managed differently. The grazed pastures
in the area were characterised by ungrazed tufts of
Juncus bufonius. Sampling of recent cattle droppings
from a pasture with an ungrazed Juncus community
shows that the cattle graze the Juncus fruits that fall
on the surrounding vegetation. The composition of
diaspores in cattle faeces may therefore also include
ungrazed species.
• The formations of dark earths in Sweden are not
connected to any specific time period but probably to
rural environments. The dark earths found in Norrköping and Karlstad were formed due to a combi-
43
J. Heimdahl
nation of recurrent alluvial deposition in areas that
were used for intense cattle handling. By the tramping of the cattle, humic soil horizons were formed
that obscured the contacts between the alluvial sand
and silt. In Norrköping the dark earth was formed
during the 13th century, in Karlstad up to the 17th
century.
• Deposition of urban strata was generally more
intense in depressions and at the base of slopes. The
causes of this seem partly to have been from a cultural need of levelling the ground due to drainage,
and partly because alluvial deposits from rain water,
snow melting and flooding were concentrated in depressions. Since alluvial deposits were concentrated
to depressions in the town, they may sometimes have
created casts of streets and lanes and backyards.
• Development of urban soil horizons was concentrated during spring, summer and autumn, when the
ground was not frozen. This is indicated by the macrofossil record originating from cattle dung in Karlstad that consists entirely of species that were grazed
at meadows. Remains of mowed winter fodder have
not been found within the preserved soils.
• In the occupational deposits of Norrköping and
Karlstad there is a significant textural trend of coarsening upwards of the minerogenic material because
the local sand and silt was used as fill in the early
phases, and more coarse sand and gravel was used in
later constructions. (This trend is also observed during field studies in Skänninge and Stockholm, and
according to many archaeologists it seems to be common in the occupational deposits of most towns.)
The shift was identified to have occurred during
the 17th century in Norrköping and during the 18th
century in Karlstad. It is probably a reflection of a
professionalisation of the urban building procedures
that apparently occurred at different times in different towns.
• Waste material does not seem to have been used
as a primary filling. Places where the dumping of
minerogenic filling material occurred were probably
secondarily used as places for waste dumping. The
different taphonomy of the urban macrofossil record
may be utilized to make interpretations of the composition of mixed and reworked depositions. Macrofossil remains may contribute to model the development of both local and regional environments.
Changes in the local urban flora may reflect both
environmental changes and interspecies competition.
When such changes occur, they can be locally used
for indirect dating of strata.
• Formation processes of urban strata are regulated by three major factors: Deposition, post-depo-
44
sitional soil formation and erosion/truncation. All
these factors may occur as both natural and cultural.
Culturally controlled factors dominate but natural
factors are always present and even dominate on
some occasions. Intentional and natural depositions
seem to have contributed to the main part of the
minerogenic material. The main part of the organic
material was successively deposited unintentionally
and unintentionally mixed into the topsoil through
tramping. Past urban environments in Norrköping
and Karlstad were geologically active and geological
processes contributed to and greatly affected the site
formation process.
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Urbanised Nature in the Past
Den urbaniserade
naturen
De äldre städernas spår
Städer är ofta byggda på resterna av sina forna
lämningar. Äldre fyllnadsmassor, husgrunder, gator,
avfallshögar och enstaka glömda och borttappade
föremål utgör s.k. stadskulturlager. Vid sidan av
arkeologiska kulturlämningar vittnar geologiska och
biologiska spår om den miljö som funnits i och omkring staden under olika perioder. Det är lätt att se
’staden’ som en motsats till ’naturen’, men miljön i
städer utgör också en ekologisk nisch för växter och
djur med särskilda krav. I staden skapas också förutsättningar för vissa geologiska processer. På samma
sätt som man kan tala om en ”urbaniserad människa/kultur” kan man också tala om en ”urbaniserad
natur”.
Traditionen att arkeologiskt gräva ut stadskulturlager är ung och uppkom när lagren, och fynden i
lagren började klassificeras som fornminnen. Före
1970-talet hade bara en handfull utgrävningar
av städer gjorts i Sverige. Stadskulturlager är ofta
stratigrafiskt komplexa och svårtolkade, och inte
sällan är de flera meter tjocka, och när arkeologin
ställdes inför dem tog utvecklingen den arkeologiska
stratigrafin fart. Man frågade sig vad alla dessa lager egentligen representerade, vad de bestod av och
hur de bildats. En central fråga för tolkningen, och
för att kunna förstå fyndmaterial och konstruktioner, blev om dessa lager var medvetet skapade, eller
tillkommit omedvetet.
I ett tidigt skede kallade man bara de omedvetet
tillkomna lagren för kulturlager och man antog att
de till stor utsträckning bildats genom att människor
hällt ut avfall på gatan och tappat saker – alltså att
ett visst omedvetet vardagslivsbeteende gav upphov
till kulturlager. På senare år har denna syn förändrats
radikalt. Alla lager som skapats av människan definierar man idag som kulturlager. Den gängse synen
är, att den övervägande delen av stadskulturlagren är
medvetet skapade. Man är idag kritisk mot synen på
den medeltida människan som boende på en ständigt
växande sophög. Ändå finns bilden av medeltidens
miljö som genomsyrad av smuts kvar i mångas medvetande, delvis på grund av synen på stadskulturlagren. Den moderna synen på stadskulturlager hänger
bl.a. samman med utvecklingen av den arkeologiska
grävtekniken. De tidiga grävteknikerna omöjliggjorde upptäckandet av s.k. avröjningar, t.ex. spår
efter städning. Modern grävteknik är bättre anpas-
sad för att tillvarata dessa typer av information som
finns bevarad i kulturlagren.
Både i Sverige och internationellt har stadskulturlager främst varit studieobjekt för arkeologer, men
de senaste decennierna har också naturvetare såsom.
biologer (arkeobotaniker) och geologer (geoarkeologer), alltmer kommit att knytas till utgrävningarna. Vanligen är det fråga om tillfälliga, i bästa fall
regelbundna, besök i fält, eller analys av jordprover
som skickas in till laboratorier. Samtidigt har praxis
inom exploateringsarkeologin (som står för nästan
alla utgrävningar i Sverige) varit att fältarbetet utförs av arkeologer, vilket innebär att den viktiga
fälttolkningen av kulturlagren, som är avgörande
för slutresultaten, nästan uteslutande görs av arkeologer. Det kan också uttryckas som så att naturvetenskapliga studier av kulturlager ofta saknat en
tillfredställande fältfas. En del av detta har berott på
outtalad praxis, en annan på uppfattningen att modern arkeologisk grävteknik är knepig att kombinera
med deltagande av naturvetare under fältarbetet.
Mot denna bakgrund kan den här avhandlingens
syfte beskrivas som: Att utveckla och tillämpa metoder för integrerat fältarbete mellan arkeologi och
kvartärgeologi/arkeobotanik, och att från ett kvartärgeologiskt/paleoekologiskt perspektiv tolka och
rekonstruera miljöutvecklingen och tillkomsten av
kulturlager i två olika städer: Norrköping och Karlstad. Jag har fältarbetat på grävningen i kvarteret
”Konstantinopel” i Norrköping sommaren 2000,
och under undersökningen av kvarteret ”Druvan” i
Karlstad hösten och vintern 2003-2004.
Utgrävningarna
Norrköping fick stadsprivilegier 1384 och är den
äldsta av de två städerna. Namnet finns omnämnt
redan 1283 som en viktig handelsplats. Staden är
byggd runt forsarna i Motala ström, där man anlagt
kvarnar och bedrivit laxfiske. Under stormaktstiden
växte staden i samband med att kronan anlade vapenfabriker där, och den blev en viktig exporthamn.
På 1660-talet skedde stora ombyggnader, gatunätet
ritades om och stora delar av den gamla bebyggelsen
revs och schaktades bort. Samtidigt omformade man
strömfåran så att den blev smalare än den varit tidigare. Ombyggnationen var så omfattande att spåren
efter det medeltida Norrköping nästan försvann helt,
och det var först 1999, under förundersökningen av
kvarteret Konstantinopel, som man hittade spår efter
den medeltida staden. Utgrävningsområdet ligger på
sluttningen ner mot Motala ström, på en plats, som
enligt äldre kartor ligger mycket nära strömmens
gamla strandkant.
55
J. Heimdahl
År 1589 grundade Hertig Karl (senare Karl IV)
Karlstad, som en strategisk utskeppningsplats mot
väster. Staden har en möjlig medeltida föregångare
som kallas ”Tingvalla”. Den är omnämnd som
marknadsplats i området, men har hittills inte lokaliserats arkeologiskt, även om man då och då hittar
lösa fynd i området, som visar att människor varit
här under medeltiden. Karlstad ligger på Vänerns
norra strand, där Klarälven har sitt aktiva delta.
Staden är byggd på själva deltaytan, vilket medför
att översvämningar har varit regelbundet förekommande i Karlstad genom historien.
Under utgrävningen i Norrköping utvecklades metoder i syfte att anpassa de kvartärgeologiska och
arkeologiska fältarbetsmetoderna till varandra. Alla
stratigrafiska tolkningar i fält gjordes parallellt, både
arkeologiskt och kvartärgeologiskt, vilket ledde till
mycket fruktbara diskussioner. Det blev uppenbart
att förutsättningarna för förståelsen av kulturlagren
kraftigt ökade vid gemensamt fältarbete. Det blev
också tydligt att varken arkeologisk eller kvartärgeologisk kompetens enskilt var tillräckligt för att
tillfredsställande tolka och förstå stadsstratigrafin.
Närvaron av de två disciplinerna bidrog till att flera
nya typer av fenomen kom att undersökas. Exempelvis lager, som bildats genom ”naturliga” geologiska processer såsom sediment bildade i vattenpölar
och som nu framträdde som laminerade (randiga)
linser i stratigrafin. Linserna användes för att spåra
äldre markytor som annars försvunnit i avröjningar
och de var vanliga i både Norrköping och Karlstad.
Dessa linser visade sig vid flera tillfällen innehålla
makro- och mikroskopiska spår efter aktiviteter som
ägt rum på nu helt försvunna markytor, och i områden som låg utanför själva undersökningsytorna.
Det verkar till exempel som om ölbryggning ägde
rum i området ovanför den sluttning, som grävdes
ut i Norrköping.
Den geologiska undersökningen i Norrköping visar
att de äldsta kulturlagren i området bestod av metertjocka fyllnadsmassor av sand och grus, som använts
för att någon gång på 1200-talet skapa en terrass på
sluttningen, kanske som ett skydd mot översvämningar av Motala ström. Fyllnadsmassorna har delvis
blivit dumpade i vatten, antagligen under en översvämning. Utan den geologiska undersökningen hade
dessa tidiga fyllnadsmassor antagligen blivit tolkade
som naturliga sediment, och inte kommit att ingå i
den arkeologiska tolkningen av platsen.
Eftersom analys av växtmakrofossil (växtrester
synliga för blotta ögat, främst frukter och frön)
tillämpades som huvudmetod utvecklades ett system
för att kontinuerligt och preliminärt analysera alla
stratigrafiska enheter och arkeologiska lämningar
56
redan i fält. På så viss kunde provtagningen effektiviseras och arkeologerna kunde få svar på vilka
växtrester som fanns i olika lager, innan de var helt
utgrävda. Förutom att ge svar på hur den lokala
floran i kvarteret såg ut, visade också analyserna
t.ex. spår av latrinavfall, kodynga, odlingsväxter
och åkerogräs, rester av ölkryddor, exotiska (importerade) växer, men också spår av hantverk som
t.ex. smidesloppor.
Växterna i Norrköping och Karlstad
Växtrester som bevarats i stadskulturlager har ett
komplext ursprung. För att kunna tolka sammansättningen av växtfossilen, måste man förstå vilka processer som lett till att de hamnat där.
Staden har en lokal flora med växter som trivs i
själva stadsmiljön och som kan avslöja hur miljön
varit på olika platser, t.ex. vilka områden som betrampats, var avfallsplatser har funnits, och vilka
områden som legat i skugga eller sol. Förändringar
i lokalfloran kan avslöja förändringar i stadsmiljön.
En stor mängd frön och frukter kommer in i staden
via djur som betat i hagar eller ätit vinterfoder slaget
på ängar. Frön och frukter i dynga ger signaler om
hur stadens omgivande hag- och ängsflora sett ut vid
olika tider. En tredje viktig fyndgrupp är frön och
frukter från odlade och insamlade växter, som förts
in i staden för bearbetning, försäljning och konsumtion. Makrofossil som hittas i spiskonstruktioner eller i latrinavfall kan ge indikationer på vilken typ
av kost som konsumerats, vilket i sin tur kan ge
antydningar om den lokala ekonomiska situationen
och klasstillhörighet hos de inneboende i kvarteret.
I Norrköping fanns tydliga tecken på att lokalfloran
skiftat karaktär genom tiden. Före stadsbebyggelsens
tillkomst verkar platsen ha utgjort en del av en betad
flodstrandäng med kvarlämnade tuvor av tågväxter och brännässlor. Längre upp i sluttningen fanns
ett naturligt strandhak utbildat i sand, och ovanpå
detta hak återfanns torrmarksväxter som sandnarv
och backtrav. Denna vegetation begravdes helt av
de metertjocka fyllnadsmassor som dumpades i sluttningen för att forma en terrass någon gång på 1200talet. Byggnader restes på denna terrass och kreatur
hölls i området, vilket ledde till att näringshalten i
marken ökade kraftigt. Större delen av marken var
förmodligen barmark till följd av intensiv kreaturstrampning, Näringskrävande växter som brännässla
och blåmålla växte förmodligen längst husväggar
och inhägnader. Likaså fanns en tramptålig flora med
t.ex. trampört på vägar och bakgårdar. Sammansättningen av den lokala flora verkar i stor utsträckning ha varit oförändrad från 1300-talet och framåt,
Urbanised Nature in the Past
men vissa förändringar kan dock spåras, i synnerhet
kring mitten av 1500-talet då djurhållningen får ge
vika för en mer hantverkspräglad miljö. Vissa örter,
t.ex. trampört och vitplister försvinner ur kvarteret,
medan andra, t.ex. bolmört och vildpersilja ökar i
betydelse. Även rester av bevuxna hustak hittades
på platsen. Innehållet i de rikliga resterna av dynga
i kulturlagren visar att boskapen betat på fuktiga
strandängar dominerade av starr och tågväxter runt
Motala ström, utanför själva staden.
Det fanns rikligt med spår av kulturväxter i Norrköping. Bland sädesslagen dominerar rågen från
1300-talet och framåt, vilket överensstämmer med
historiska uppgifter om Östergötland som en del av
dåtidens ”rågbälte”. Det indikerar kanske också att
den lokala konsumtionen präglades av lokalt odlade grödor. En annan intressant fyndgrupp utgörs
av ölkryddor som hittas i lämningar från 1300-talet
och framåt. Förutom den populära humlen verkar
ölet fram till 1550-talet också ha kryddats med pors,
men därefter verkar humlen ha blivit den helt dominerande ölkryddan. Ytterligare en intressant växt i
sammanhanget är älggräs, som är överrespresenterat
i prover, som också innehåller humle och pors. Älggräset användes som öl-/mjödkrydda under vikingatiden, men inget är hittills känt om eventuell användning under medeltid, eller i kombination med humle
och pors. Från 1550-talet ökar fynden av exotiska
och exklusiva frukter som vindruva och fikon, vilket
väl överensstämmer med kvarterets utveckling till
borgarkvarter. Av särskilt intresse är fyndet av frön
från bondtobak. Eftersom import av tobak innebär
import av blad, och eftersom ingen bladvävnad hittades tillsammans med tobaksfröerna, indikerar dessa med stor sannolikhet att tobaksodling ägt rum i
eller omkring Norrköping. Tobaksodling blev vanlig
i Sverige under början av 1700-talet. Dessförinnan
odlades växten i liten skala, mest som kuriosum, eller
som medicinalväxt. Den tidigaste Svenska odlingen
av bondtobak känd från historiska källor finns angiven 1632 från Uppsala slottsträdgård. Tobaksfynden
från Norrköping dateras med hjälp av stratigrafin
och artefakttypologi till mellan 1560 och 1660, men
den tidigare delen av perioden, alltså ca 1560-1610
är troligast. Stämmer denna datering är detta spåren
efter den tidigaste odlingen av tobak i Sverige.
Spåren efter den tidigaste lokala floran i Karlstad
hittades i deltasedimenten på en meters djup. De visar
att deltat kring Kristi födelse varit skogsbevuxet med
björk och al, och att snår av ljuskrävande växter som
slån och hallon vuxit längst stränderna av de slingrande älvkanalerna. Någon gång, troligtvis under
medeltiden röjs skogen och deltat omvandlades till
betesmark, karaktäriserad av tågtuvor. Någon gång
mellan 1000- och 1600-talet började man hålla
boskap i någon form av fållor och vegetationen på
den trampstörda marken ersattes lokalt av en ruderatflora dominerad av revormstörel och pilört. De
omgivande fuktängarna dominerades alltjämt av tåg.
När hus började byggas på platsen i slutet av 1500talet tillkom näringskrävande växter (t.ex. nässlor,
blåmålla och tiggarranunkel) och tramptåliga växter
(ex. groblad och trampört). I mitten av 1600-talet
försvann den tidigare dominerande revormstöreln
och mer ovanliga växter uppträdde, såsom kålsenap
och gat- eller stinkmålla, vilka idag blott sporadiskt
förekommer längst hamnar på västkusten. Förekomsten av dessa växter visar på Karlstads dåvarande
betydelse som utskeppningshamn till västkusten. Likaså verkar många växter som idag har sitt utbredningsområde begränsat söder om Vänern ha förekommit i Karlstads lokalflora på 1600-1700-talet.
I lämningarna av ett litet nedbrunnet stall i Karlstad hittades en sammanpressat laggkärl med rester
av bevarat hö, som satt fastklibbat på kärlets insida.
Jämförelser av innehållet i detta hö med innehållet i den kreatursdynga som fanns på golvet i stallet visar radikalt olika sammansättning, och ger en
unik möjlighet att separat urskilja ängs- och betesmarksmiljöerna runt 1600-talets Karlstad. Resterna
i spannen består med all sannolikhet av hö från flera
olika ängar, och visar att foder tagits från både hävdade och ohävdade ängar. Sannolikt motsvarar sammansättningen den man kan förvänta sig finna i det
vinterfoder som använts lokalt. Sammansättningen
av dyngan på stallgolvet är däremot en helt annan
och domineras av tåg, och liknar all annan dynga
som hittades i Karlstads kulturlager. Detta innebär
förmodligen att sammansättningen av dyngan representerar betad hagmark och inte slaget foder. Det
innebär att det lilla stallet sannolikt inte använts för
vinterstallning av djur, utan att djuren som hållits där
nyligen varit på sensommar eller höstbete, förmodligen inför slakt. Idén om funktionen av det lilla stallet
som slakteri förstärks av att en grop i närheten innehöll koskallar, vilket därmed skulle knyta gropen
till stallbyggnaden. Prover tagna från modern dynga
på Mariebergs strandängar visar att frukter från
tågväxter är mycket rikligt förekommande, trots att
djuren undviker denna växt som lämnas kvar som
tuvor. Djuren får i sig tågfrukterna genom att dessa
sprids från tuvorna till den omgivande betade vegetationen.
Också i Karlstad gjordes rikligt med fynd av rester
efter odlade och insamlade växter. Liksom i Norrköping dominerar det lokalt odlade sädesslaget, i
detta fall havre. Spår av insamlade frukter och bär,
bl.a. björnbär, hallon, smultron och blåhallon, före-
57
J. Heimdahl
kommer rikligt. I lager från 1700-talet förekommer
också spår av parksmultron, en äldre odlingsväxt som
sedermera kom att ersättas av jordgubben. Ett fynd
av kryddpeppar från tidigt 1600-tal utgör ett intressant exempel på en mer exklusiv växt, som nyligen
börjat öka i användning på kontinenten under denna
tid. Endast två arkeologiska fynd av denna växt är tidigare kända från Europa. I resterna av ett nedbrunnet hus från 1700-talet hittades ett antal tobaksfrön.
Tobaksodlingen i Karlstad kan knytas till en specifik
historisk person: Gustav Clareen, som odlade tobak
i trakten mellan 1741 och 1772. Fyndet av tobaken i
detta nedbrunna hus skulle därmed kunna knyta det
till stadsbranden den 8 juni 1752.
Lagrens och horisonternas tillkomst
Det är tydligt att bildningen av kulturlager både i
Norrköping och Karlstad starkt influerats av de
rådande lokala topografiska och geologiska förutsättningarna. Den sluttande topografin i Norrköping
skapade förutsättningar för vattentranport av material utför sluttningen så att finsand och silt ansamlades
i de lägre belägna delarna av kvarteret. Ansamlandet
av vattentransporterat slam var så omfattande att
decimetertjocka lager bildades och fyllde ut gränder
och gator mellan husen och kom att skapa ett slags
negativa avgjutningar av gatunätet och angränsande
byggnader. Det blev därigenom möjligt att, genom
studier av det vattenavsatta sedimentets form, finna
avgjutningar av föremål och konstruktioner som
fanns på platsen när slammet avsattes men som nu
är försvunna.
När slammet avsattes i gränderna och på gatorna
i stadens lägre belägna delar, ledde de till dräneringsproblem. Detta löstes genom att nya byggnader restes
på upphöjda grunder över gatuplanet, vilket skapade
nya sänkor av gatunätet, och snart var problemet
tillbaka när nytt slam täppte till gatorna, varpå husgrunderna ånyo fick höjas. Följden blev ett cykliskt
förlopp i en miljö där erosionskänsliga jordmassor
exponerades. Erosion genom regnfall och slamavsättning ledde till en viss kulturell respons som innebar
att nya jordmassor exponerades. Förekomsten av
denna natur-kulturcykel skulle kunna förklara de
tjocka kulturlagren och den rikliga förekomsten av
vattenavsatta sediment i städernas svackor.
Undersökningar av texturen (kornstorlekssammansättningen) i materialet som använts i husgrunder vid olika tidpunkter i stadens historia, visar
liknande tendenser för Norrköping och Karlstad. I
det tidiga skedet användes finkornigt material (silt
och finsand) som hämtats lokalt (förmodligen inte
mer än några meter bort). I senare tid skedde en
58
omsvängning, först med användning av en kombination av lokalt finkornigt material och grövre material, och sedermera till bruk av grovsand och grus,
som i Karlstad måste ha hämtades från mer avlägsna
täkter. Denna förändring är tolkad som en professionalisering av byggandet. Från att husbyggarna
varit inflyttande bönder, går ansvaret över till ett
byggarskrå med andra traditioner. Det finkorniga
materialet i grunderna kan förklaras av att det på
landsbygden, där husen mer fritt kunnat placeras
på dränerade platser, funnits en tradition av att ha
betraktat grundmaterialet främst som köldisolering,
medan de professionella byggarna i städerna främst
såg det som en stabil infiltrationsbädd. Professionaliseringen av byggandet sker vid olika tidpunkter i de
två städerna, i Norrköping sker den omkring 1600
och i Karlstad omkring 1700. Förändringen leder till
att de yngre kulturlagren är bättre dränerade vilket
gör att organiskt material bevaras sämre än i de
äldre lagren. Det grövre materialet står också emot
erosion bättre, varför också förekomsten av vattentransporterade lager minskar.
Vid studierna av stadsstratigrafi har jag funnit
det nödvändigt att skilja mellan två huvudtyper av
stratigrafiska enheter (strata): lager och horisonter.
Med lager, eller depositioner, menas här ett material
som transporteras och deponerats ovanpå en yta och
kommit att bilda en sammanhängande enhet. Med
en horisont menas en del av markskiktet (oftast de
översta centimetrarna) som påverkats av den miljö
som existerat ovanför. Det kan t.ex. vara fråga om
markskiktet som påverkats av växtrötter, eller att
marken trampats. Man kan också tala om lagren
som depositionella och horisonterna som postdepositionella stratigrafisk enheter. Depositionerna, eller
lagren är i allmänhet bildade under kortare tidsperioder, från några sekunder upp till ett antal veckor,
medan horisonterna ofta är bildade under betydligt
längre tidsperioder. Många tramphorisonter har förmodligen utbildats under flera års tid.
I syfte att skapa en teoretisk modell över hur stadskulturlager bildas kan de två huvudtyperna av strata
kombineras med den arkeologiska frågeställningen
om vilka enheter som bildats under medvetna och
omedvetna processer. För att alla lager i stadsstratigrafin skall täckas in krävs också att man frågar sig
vilka enheter som bildats genom naturliga processer.
Modellen, som framträder, är ett nätverk av medvetna, omedvetna och naturliga handlingar, aktiviteter och processer som bidrar till bildning av olika
typer av lager och horisonter, men också till deras
försvinnande. Modellen möjliggör också en direkt
tolkning av de handlingar, händelser och förutsättningar som ligger bakom flertalet stadsstratigrafiska
Urbanised Nature in the Past
enheter.
Analyserna av makrofossil ger också indikationer
på hur kulturlagren och tramphorisonterna bildas. I
Karlstad, där det varit möjligt att skilja mellan vinterfoder och sommar-/höstbete, är det uppenbart att
dyngan bevarad i stadskulturlagren domineras av
det senare. Detta tyder på att bildandet av tramphorisonter hämmades vintertid då marken var frusen.
Frånvaron av spår av vinterfoder indikerar också att
den dynga, som avsatts i staden vintertid, antagligen
hunnit städats undan innan marken tinade och den
trampades ner i marken. Detta antyder i sin tur på
att gatorna i Karlstad städades regelbundet.
Det sammantagna intrycket av bildningen av stadskulturlager är ett komplext system av kulturella
och naturliga processer. De mänskliga aktiviteterna
i de äldre städerna skapade förutsättningar för en
mängd geologiska processer som i sin tur gav upphov till motåtgärder. Den geologiska miljön i de
äldre städerna kan både betraktas som aktiverad och
i viss mån kontrollerad av människan, samtidigt som
människan i viss mån styrts av geologiska förutsättningar och påverkats av geologiska processer.
Tack!
Som den strikta men förvirrade forskare jag nu kommit att bli, har jag valt att dela in detta tack till olika
personer som riktat till olika skaror. Dessa är fem till
antalet och individerna inom dem har haft betydelse
för avhandlingen på olika sätt.
Jag vill inleda med att tacka den första skaran,
nämligen mina handledare och mentorer som alltid
funnits där när jag behövt dem, först min huvudhandledare Ann-Marie Robertsson. En gång för snart tio
år sedan bad hon mig vänligt men bestämt återgå
till övningspreparaten när jag försökte se hur mina
anteckningar i blyerts såg ut genom mikroskopet.
Sedan dess har jag alltid haft stor respekt för vad
hon sagt. Hon har genom åren oförtröttligt stöttat
mig med sin kunskap, sitt tålamod och sitt kulturella
engagemang. Sedan kommer jag till mina biträdande
handledare i bokstavsordning: Ann-Marie Hansson (Arkeologiska forskningslaboratoriet) ledde mig
genom grinden till arkeobotanikens ängder. Förutom att hon alltid varit mycket generös med sitt kunnande, gav hon mig dessutom en frack som jag sedermera gifte mig i! Jan Lundqvist har handlett mig
i de sedimentologiska frågorna och med outsägligt
glatt humör hjälpt mig på många sätt. Hans öppenhet och förmåga att ständigt framhålla hur lite han
vet (trotts att han vet mest av alla) har inspirerat mig
mycket. Mats Regnell var den som först ledde mig
över arkeobotanikens ängder. Hans osvikliga tro
på mig har många gånger fått mig att må bättre än
jag förtjänat. Slutligen vill jag i denna skara också
tacka Claes Hättestrand, som inte varit handledare
i formell bemärkelse, men som ”utomstående forskare” tog sig tid att läsa min kappa och som kommit med många värdefulla kommentarer.
Den andra skaran jag vill tacka är de arkeologer
som tagit hand om mig under fältarbetena. I Norrköping, där jag tog mina första stapplande steg
bland kulturlagren, och först hade svårt att förstå
vad det var jag såg, leddes utgrävningen av Hanna
Mennander och Pär Karlsson (UV- öst). De gav mig
sprit och värme och såg till att jag hade det bra. De
blev sedermera mina medförfattare och genom dem
har många dörrar till den arkeologiska världen öppnats för mig. Också de andra arkeologerna i Norrköpingsgropen Anna, Annelie, Clas, Jasmine och
Kattis är jag skyldig ett stort tack för allt socialt utbyte av både och kunskapsmässigt utbyte. I Karlstad
leddes utgrävningen av Martin Karlsson (Värmlands
museum) och Kerstin Fogelberg (UV-bergslagen) som
tillsammans med Ebba och Björn gjorde arbetet och
vistelsen där mycket angenäm. Jag vill också tacka
Kerstin och Ebba för att de delade sin kvart med mig,
och Kerstin för att hon hjälpt mig med språket i en
av artiklarna. Andra arkeologer som betytt mycket
för mig i sammanhanget, är Ingrid Dyhlén-Täckman
på Stockholm stadsmuseum, Mattias Bäck och Johan Anund på UV-mitt, Stefan Larsson på UV-syd,
Ulrika Söderlind på Stockholms universitet, Rickard
Hedvall, Karin Lindeblad, Maria Petersson, Magnus
Stibéus och Göran Tagesson på UV-öst. De har alla
på sitt sätt bidragit till att jag kunnat utveckla idéerna i denna avhandling.
Till den tredje skaran räknar jag mina arbetskamrater. De har alla hjälpt och stöttat mig på olika sätt.
Särskilt vill jag nämna Barbara Wohlfarth för att hon
visat mig stort förtroende och stöttat mig sen den dag
hon började leda avdelningen. Urve Miller för hennes
brinnande tro på tvärvetenskap och hennes uppmuntran och stöd genom åren. Tack vare hennes har jag
kunnat delta i många konferenser och symposier
runt Östersjön. Lars Brunnberg har delat med sig av
sin pedologiska kunskap och förgyllt åren genom att
ösa ur sin kopiösa fatabur med anekdoter. Jan Risberg har hjälpt mig med diatomékunskaper och Sven
Karlsson med pollenkunskaper. De har båda med sin
erfarenhet av arkeologer också kunnat le överseende
när jag stundom farit ut i frustration över de språkförbistringar som råder mellan kvartärgeologer och
arkeologer. Helena Alexandersson höll mig i handen
59
J. Heimdahl
när jag började fumla med layoutprogrammet. Jag
vill också tacka dem som varit mina doktorandkolleger genom åren. Anna, Greger, Martina, Kristian,
Tiit, Gun, Anders, Prem, Linda, Sofia, Joshi, Dannile, Jonas, Amélie och Tim som jag haft mycket roligt med. Särskilt vill jag tacka Anders Borgmark för
alla spel han laddat ner till mig, all öl han trugat i
mig, alla efterrätter han lagat och allt kul vi haft tillsammans, och Jonas Bergman för alla ickegeologiska
diskussioner, all badminton och allt bus i källaren.
Jag vill också tacka Danny, Siwan, Tina, Martin och
Kerstin som hjälpt mig med språket i denna avhandling, och Anna-Lena Anderberg (Naturhistoriska
riksmuseet) som hjälpt mig med identifiering av vissa
fröer som inte ville ge sig tillkänna.
Ekonomiskt stöd har erhållits från Gerhard De
Geer’s stiftelse. Dateringar har bekostats av Swedish Match North Europé AB via Inga Junhem som
också entusiastiskt hjälpte mig med referenser om
äldre svensk tobaksodling.
Den fjärde kategorin är mina nära vänner som bidragit till min lyckliga status även sedan jag lämnat
det otroligt stimulerande dagsverket av att sortera
tusentals millimeterstora frön i mycket små burkar.
Främst vill jag tacka min vän och före detta sambo
Erik som i sanning outat mitt humanist-jag och för-
60
gyllt min tillvaro med långa diskussioner om varia,
filosofi, arkitektur, historia, Victorian ways of Firing
Automatically och kostymer. Sedan alla i den mytomspunna Mystiska klubben, däri, förutom Erik,
också Danny, Axel, Helena, Caroline, Lotta och Jonas ingår. Tack vare dem har jag gjort många värdefulla internationella bekantskaper som t.ex. Walter
Talcott, Patricia Herrington och Robert Tindale,
vilka alla bidragit till utvecklingen av detta arbete.
Det femte kategorin att tacka är min släkt för att
de alltid stöttat mig och, helt okritiskt, tycker allt
jag gör är bra. Mina föräldrar vill jag tacka för att
de alltid uppmuntrat mitt petimeterintresse för naturen, och mina systrar för att de stått ut med (och
fortfarande står ut med) att jag på ett självgott sätt
försökt imponera på dem med dessa petimeterkunskaper. Sist, men kanske ändå främst, vill jag tacka
min fru Jenny för att hon den där kulna höstkvällen
för fem år sedan repade mod och frågade om hon
fick se mitt ”laboratorium”. Det fick hon, och jag
saknar ord att tacka henne för det.
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