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RESEARCH PROGRAMME
LATERES COCTILES – THE EARLY USE OF FIRED BRICKS IN EUROPE
INTRODUCTION
From the beginning of the first century of the Christian era standardised fired bricks were
produced in large quantities in and about Rome. This building material soon spread all over
the Roman Empire and gained an important role in Roman architecture, thereby significantly
affecting building traditions also in later periods. Consequently, different aspects of Roman
bricks have been thoroughly studied throughout the 19th and 20th centuries and still occupy a
considerable number of scholars. Very little, however, is known about the distribution,
development and use of pre-Roman bricks in Europe. Recorded finds indicate that fired bricks
were first introduced in the north Aegean in the mid 4th century BCE. Within a few decades
after the first appearance of this innovation, it had spread to numerous places around the
Mediterranean. For a long time, however, the use of fired bricks was limited and sporadic,
and it took more than 300 years before the new building material made its final breakthrough.
SPECIFIC AIMS
The general purpose of this project is to bring to attention and re-evaluate an important
archaeological material, early fired bricks, but also to identify decisive factors behind the
development and diffusion of technical innovations in antiquity. The specific aims of the
project are:
1. To establish the use of fired bricks in the Mediterranean area before the introduction of
standardised Roman bricks at the beginning of the Christian era (the rule of Augustus). By
compiling and publishing all reported finds of early fired bricks, a practically unknown
material will be made available to the scholarly community. Despite the importance of bricks
for ancient construction and the history of architecture, general treatises on this subject only
briefly mention this early stage of the development – a comprehensive overview is still
lacking. This has resulted in a distorted view on the use of fired bricks in Greek architecture
and an incomplete understanding of the origin of Roman bricks. A complete catalogue would
offer a useful comparative tool for archaeologists in the field, as well as architectural
historians.
2. To analyse the early use of fired bricks in the Mediterranean area from a technical and
functional point of view, and investigate its consequences for the development of building
technology. The role of fired bricks in Greek architecture is barely studied and practically
unknown. In the study of ancient architecture, both within classical archaeology and art
history, there has been a bias towards monumental buildings in stone. A shift of focus towards
brick architecture might offer new insights regarding economic and social aspects of the
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ancient building industry, but also further our understanding of technological processes and
innovativeness.
3. To formulate a model for the diffusion of fired bricks up to the beginning of the Christian
era (the rule of Augustus). Diffusion is a central, but also debated, concept in archaeology.
For a long period in the history of archaeological research, consequences of diffusion in terms
of cultural change constituted an important theme. Despite this, the mechanisms behind
diffusion are still poorly known. How were new ideas disseminated and adopted in past
times? How did diffusion actually work? A study of the use of fired bricks is particularly well
suited to provide answers to these questions, since the diffusion of bricks was both irregular
and extended over a long period of time. Thus, we can outline different stages of the process:
periods of rapid growth, discontinuance, re-invention and breakthrough. A close study of the
early use of fired bricks, combined with modern approaches in sociology and network
analysis, may contribute to the theory of diffusion of innovations on a general level.
HISTORY OF RESEARCH
The project combines two different topics with separate histories of research: the early use
and development of fired bricks in the Graeco-Roman world (including neighbouring areas),
which belongs to the field of Classical archaeology; and diffusion of innovations, which has
been discussed within a wide range of disciplines (pre-historic archaeology, anthropology,
geography, sociology etc.).
Early bricks
Fired bricks were manufactured and used in Mesopotamia already from the third millennium
BCE and onwards. The development and use of bricks in this area can be traced at least to the
7th century BCE, and it is probable that there was some sort of continuity down into Classical
times (Wright 2005). However, the exact nature of the connections between Mesopotamian
bricks and later Greek bricks is not clear. Unfortunately, this issue must be left out of the
proposed project, as the amount of the comparative material would become overwhelming.
On the European continent fired bricks first appeared in the second half of the 4th
century BCE, but the exact date and place of origin is not yet established. Most finds are only
treated in passing in the archaeological reports and references to parallel finds are rare.
General studies on the early use of fired bricks in the Mediterranean area are also limited,
either geographically or chronologically (Čičikova 1957; Wilson 1979), and usually aim at
questions that are peripheral to this project (Mingazzini 1954; Coarelli 2000). The existence
of Greek fired bricks has for a long time been acknowledged, for example in handbooks and
manuals on ancient architecture (Robertson 1945; Blake 1947; Dinsmoor 1950; Lugli 1957;
Martin 1965; Hellmann 2002; Wright 2005), but the treatment of the subject is superficial and
based on a few arbitrary finds. This can be seen both as a cause and a consequence of a
widespread underestimation of the significance of this material. As no efforts have been made
in order to compile the growing number of (seemingly isolated) finds, the status of our
knowledge is still, more or less, on the same level as it was 60 years ago. One of the most
important contributions in recent years was made by F. Coarelli (2000), who in a short paper
drew attention to the Hellenistic tradition of this building material on the Italian peninsular.
H. Gerding (2006) has presented a preliminary assessment of the general development
and also contributed to our understanding of the introduction of fired bricks in Augustan
Rome (Gerding 2002; 2008). Generally, however, the background and origin of Roman bricks
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have been left un-investigated and the relationship between Roman and Hellenistic (Greek
and Etruscan) bricks is still poorly understood (Wilson 1979, 15; Wright 2005, 115). On the
other hand, many archaeologists, working on sites where early fired bricks are encountered,
may have far-ranging experience and deep knowledge of this material, although their main
scientific efforts are directed on other pursuits.
Diffusion of innovations
An innovation can be many things – an idea, a usage, an artefact or a technology – as long as
it is perceived as something new. However, it is necessary to distinguish between invention
and innovation. The former implies a novelty in absolute terms – a creation or discovery –
whereas the latter has a relative meaning. That is, everything is an innovation for those who
see it, or hear about it, for the first time. By diffusion is generally meant the transferral of an
innovation from one individual to another – a social process that may result either in the
adoption or rejection of the innovation. The expression can be used to designate processes
taking place within a social system, but also between different groups or ‘cultures’.
Diffusion has always been an important theme within archaeology and anthropology
(see e.g. Dunnel 1990). The longstanding debate regarding the causes of cultural change, for
example, involves the consequences of diffusion. Diffusion has also been contrasted with
other possible modes of dispersal of cultural traits: evolution, migration, copying without
interaction etc. When discussing the process of diffusion, archaeologists have usually been
concerned with the motives behind adoption and the reasons for successful or un-successful
dissemination of particular innovations. European archaeologists have tented to favour sociocultural aspects of transferral of information (e.g. the importance of prestige) whereas their
American colleagues, at times, have concentrated on the functionality of innovations. In
ancient history, on the other hand, scholars have often focused on attitudes towards
technological innovations and the consequences of these innovations for production and
economical growth (Finley 1965; Archibald, Davies & Gabrielsen 2005). Two recent papers,
however, treat ancient innovations (Megarian mould-made bowls and lead-glazed pottery) in
a way that has affinities with this project, exploring possible factors behind the diffusion
process (Rotroff 2006; Green 2007).
Within the social sciences various aspects of diffusion have been investigated for more
than a hundred years (Rogers 1995). The work of T. Hägerstrand (1953) has had a wide
influence on Swedish archaeology, but the methodology of these disciplines has rarely been
applied to Classical archaeology. Furthermore, during the last ten years there has been an
explosion in our understanding of different types of networks and the processes that may
occur in them (Watts & Strogatz 1998; Strogatz 2001; Barabási 2002; Strogatz 2003; Watts
2004). These recent advances within physics and mathematics have generated new insights,
which are relevant also to the study of diffusion of innovation.
DESCRIPTION OF THE PROJECT
The project has two team members: Henrik Gerding (Docent in Classical archaeology and
ancient history), who is the main applicant, and Per Östborn (PhD in mathematical physics).
Gerding will commit 75% of full-time to the project and Östborn 15%. This collaboration
combines knowledge in ancient architecture and building technology with the experience of
modelling and analysis of complex systems (see CV and list of publications). The duration of
the project is estimated to three years.
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Data collection and compilation
A large part of the work consists of the collection and compilation of archaeological data that
will form the basis for subsequent analyses. The bulk of this data will be obtained from
published material. A rudimentary list of finds of early fired bricks has already been created,
and some preliminary results were presented at an international conference in Boston 2003
(Gerding 2006) and also at symposia in Athens 2007 and Lund 2008. To date, the list includes
about 80 sites around the Mediterranean, where early fired bricks have been found, and ca 130
different contexts. This list provides a valuable and unprecedented overview, but is not
exhaustive. In order to make a systematic catalogue, the contents of the list have to be
supplemented, correlated and verified. In some cases, this can be done by collaborating with
the archaeologists responsible for the excavations where early bricks have been encountered,
but in most instances, when the finds were made many years ago, supplementary field studies
has to be undertaken within the project. Of course, this is only possible at those sites where
the material is still available. By concentrating the field work to three trips, each covering
some key areas (north Aegean and Epirus; south Italy and Sicily; north and central Italy), the
data collection will made be more efficient. The number of items on the list will continue to
grow during the project, but at a decreasing rate. In order to estimate the amount of finds that
may be overlooked, all reports from a number of randomly chosen archaeological sites will be
systematically screened. If these tests turn out to be fruitful, they can be extended as a means
of supplementing the list.
Core data on all brick finds (description, dimensions, stamps, find location, context,
function, building technique, date etc.) will be registered in a database, which can be linked to
a geographical information system (GIS). This will facilitate graphic presentations, such as
distribution maps and diagrams, but also the production and analysis of statistic information.
Care has to be taken to compensate for the different origin and varying quality of the data. In
the published catalogue these consideration will be related, as well as discussions regarding
find circumstances, interpretations and evidence for dating.
Analysis of development and use of fired bricks
Fired bricks may be seen as a ‘technology cluster’ rather than a single innovation. That is,
different ways of making and using bricks can be treated as separate innovations. However, it
can be argued, on the basis of preliminary evidence, that the different usages are strongly
connected and that they all form part of a single developmental process. This process will be
explored through the collected data of the catalogue. Shape, size and firing are the most
palpable outward characteristics of bricks, and they may reveal information on production and
economy of use. For an understanding of the development and spread of bricks, however, it is
more rewarding to study the context; how the bricks were used and in what kinds of
buildings. It is important to determine the structural function of the bricks and the manner of
construction. Thereby we can make comparisons to other building materials and technical
solutions, and better grasp the motives behind the use. It will also make it possible to
elucidate the relationship between different finds. The dating of each find is also important for
the understanding of the development and spread. Extant dates must be critically evaluated
and in some case it may be useful to make thermoluminescence (TL) measurements. This
dating technique has been refined in recent years and shown to be particularly well suited for
dating brick walls (Martini & Sibilia 2006).
As a background to the key material it is also necessary to consider prior use and
development of architectural terracotta, and the economy and logistics of production of
building materials (prices, capacity of kilns etc.). In this and other regards historical sources
will be useful. However, these investigations will only constitute minor parts of the study.
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Analysis of diffusion of fired bricks
The third aim of the project is to understand the process behind the spread of fired bricks.
This process is most likely to be one of diffusion, although a null hypothesis must be
considered. The traditional model of the innovation-decision process, developed by E. Rogers
(1995), is taken as a starting point for the methodological approach. This model highlights the
importance, not only of prior conditions (e.g. perceived needs, social norms, innovativeness)
and perceived characteristics of the innovation (e.g. relative advantage, compatibility,
visibility), but also of communication channels. Rogers’ model also underlines the difference
between knowledge of an innovation and adoption of an innovation in a way that has not
always been clearly recognised in studies of diffusion in archaeology. This distinction is
evident in the case of the spread of fired bricks and has implications for the analysis, as well
as the historical interpretation of the process. Furthermore, it is noted that social affinity
between adopter and agent is crucial for the success of the diffusion process.
Recent advances within network theory support the idea that the nature of the social
networks, in which diffusion takes place, significantly influences the results of the process,
and also provide new mathematical tools for network analysis (Valente 1995; Watts &
Strogatz 1998; Strogatz 2001; Watts 2002; Watts 2004). These methods have been applied on
a wide range of problems in different disciplines (sociology, economy, biology etc.). In
archaeology, however, they have only recently been introduced (Graham 2006a & b). Three
main approaches will be explored:
A) Data analysis from a network perspective
The diffusion of innovations is often assumed to take place on an underlying network. One
may consider a physical network of roads and trade routes, along which new ideas and
influences may travel. One may also speak of a social network of personal contacts between
users or decision makers. The problem with the study of the diffusion of innovations in past
times is that often, neither of these networks is known. The only information available
consists of archaeological finds, representing the distribution of the innovation.
Even if we cannot reconstruct the actual physical or social networks with this
information, we can hope to reconstruct their structure. A lesson learned from the modern
science of networks is that the structure of a network to a large extent determines the outcome
of the processes taking place in the network. The structure may even put a constraint to the
spectrum of possible processes. Thus, knowledge of the network structure may be valuable in
the efforts to understand the diffusion process. With this in mind, we will develop methods to
construct phenomenological networks from available data. Such networks could be useful in
many different contexts, not just in the analysis of the diffusion of early fired bricks.
However, they should be seen as a complement to the qualitative analysis.
A network consists of nodes and edges, connecting some of these nodes. Here, the nodes
are the find locations of fired bricks. For most of these locations, there will be information
about brick shape, size, context, function, date, and so on, defining a set of variables. For each
variable, a network can be constructed where two nodes are connected by an edge if the value
of the variable is the same. Two or more such network may be added to form hyper networks.
Networks can also be subtracted, in which case two nodes are connected by an edge only if
the networks to be subtracted all have an edge linking the two nodes. In this way, causally
well connected clusters of brick usage may be identified, as well as weaker causal links
connecting such clusters. These networks can guide the construction of a probable causal
network, describing the diffusion process, in contrast to the underlying physical or social
networks. A causal network should be similar to the underlying network in the sense that the
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former can be seen as a subset of the latter. Thus it can be argued that they share the same
structure.
As a special case of a phenomenological network, we will consider temporal networks.
The suggested dates of the finds are often inexact. However, a probable time interval can
often be estimated. We let two nodes be connected by an edge when these time intervals
overlap. By continuously increasing or decreasing the time interval, we can interpolate
between a fully connected network (all nodes are connected to all the others) and a completely
fragmented network (all nodes are isolated). Of special interest is the critical point at which
the network fragments into two or more clusters as the time window shrinks. Assuming that
we have a single, global diffusion process, and given that it is slow, we may hypothesize that
the temporal network just above this point reflects a ‘true’ causal network, at least on a
structural level. By adjusting the time window, the lack of a complete data set can be
compensated for. That is, missing information about brick buildings in a given region at a
given time tend to fragment a phenomenological causal network, but this fragmentation
tendency can be compensated for by allowing a more generous time window of influence.
B) Analysis of network structures
Characteristic network measures, such as clustering or mean path length, may be computed.
This enables the classification of the network and can be used for comparing different
diffusion processes.
C) Modelling of the diffusion process
Preliminary results indicate that the dissemination of fired bricks followed a pattern that is
common to many other technical innovations in historical periods. One aspect of this ‘typical’
behaviour is the relatively long period of limited use before diffusion finally takes off (cf.
Rotroff 2006; Green 2007). This prolonged state of restricted use, ultimately leading to global
acceptance, appears to represent a stable phase rather than an equivocal tipping point. The
question is: If the innovations had relative advantages, why did it take so long for them to
gain widespread acceptance, and if they did not, why did they continue to be used?
We intend to work on two levels: investigating the main factors behind the development
and diffusion of fired bricks indicated by the contextual analysis; and exploring the dynamics
behind the system’s behaviour through modelling and simulation. One way of doing this is to
create simple models that capture the observed behaviour of the process. Such models would
allow a number of possible factors to be evaluated, involving the attributes and dynamics of
social networks, but also the interaction between supply and demand (cf. Wilson 2006, 228).
Two phenomena in particular, discontinuance and re-invention (i.e. modification) of
innovations, which frequent occur in the innovation-decision process (Rogers 1995, 163),
may have played an important role. We will also investigate the possible relevance of
awareness of actual use of an innovation in the proximity of the adaptor.
PRELIMINARY RESULTS
Preliminary work shows that the use of fired bricks in the 4th and 3rd centuries BCE was
more extensive than has been realised. The introduction of bricks in Europe seems to be
connected to monumental sepulchral architecture in Thrace (Bulgaria) where underground
tombs were decorated with interior wall paintings. Wall plaster adhere better to brick than to
stone (Sandin 1985), and the ability of bricks to absorb large quantities of moisture protected
the paintings from infiltrating water. The further spread of the bricks is strongly related to
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particular modes of use in sepulchral and military architecture, but also to other technical
innovations (e.g. the voussoir arch). The spread most probably corresponds to diffusion,
rather than independent inventions. Contrary to current opinion, the connection between early
Hellenistic bricks and Roman bricks can be established by ‘missing links’ and overlapping
functional traits. This is probably mirrored by a distinction in the use of words by Augustan
and early Imperial writers, which has not been noted before: whereas testae signify the new
‘Roman’ bricks, lateres coctiles probably stand for the old kind of ‘Hellenistic’ bricks.
SCIENTIFIC IMPLICATIONS
This project will, for the first time, present a comprehensive overview of the early use of fired
bricks in Europe. Thereby, it will also contribute to our understanding of the origin and early
development of an important European building tradition. A comparative catalogue of all
known finds of Hellenistic bricks, together with an exhaustive analysis, will provide a
valuable tool for interpreting and dating future finds. The analysis of the diffusion of early
fired bricks may provide new insights both on a structural and a historical level. Hopefully, it
will result in a more complete understanding of the mechanisms behind the diffusion of
innovations in antiquity. Network modelling may also highlight changes in social structure in
the Hellenistic period (323–31 BCE), particularly regarding the intensification of international
contacts and the emergence of large cosmopolite groups outside the aristocratic elite (e.g.
professional mercenaries) – what could be described as an early globalisation. The study may
also show how local networks (e.g. between artisans and producers of building materials)
interrelated with global trends.
TIME PLAN AND PUBLICATION STRATEGY
The greater part of the work on the database, which consists of compiling published material,
will probably be concluded within the first year (2010). The total number of entries is
estimated to be in the order of 200–250 finds. This data, however, have to be supplemented
by field observations, carried out also during the following year (2011). One field trip is
scheduled for 2010 and a further two for 2011. The context of each brick find will be
investigated as far as possible, and issues regarding the economy and logistics of brick
production will be followed up, using historical and ethno-archaeological sources. In the third
year (2012) the contents of the database will be re-structured into a publishable catalogue and
chapters on the distribution, development and function of early fired bricks finalised. A
couple of months have to be set aside for completing distribution maps and other illustrations
Parallel to this work, models for network analysis will be created and a useful
methodology for their application tried out. Once the dataset is complete, towards the end of
the second year, the network analysis can commence. The result of the combined efforts of
contextual and quantitative analyses will be discussed in chapters on the diffusion of early
fired bricks, and of innovations in general.
Two different publication strategies will be considered: 1) Catalogue and text are
published together in a monograph; the catalogue is also deposited in an open digital archive.
2) An abbreviated catalogue and text are divided between two or three long articles, submitted
to international peer-reviewed periodicals; the full catalogue is deposited in an open digital
archive together with a down-loadable database. In either case, a paper describing the
methods for network analysis, used in the project, will be published separately. Many aspects
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of the project (historical, architectural and mathematical) will be of popular interest. Both
members of the project also have a genuine (and well documented) interest in transmitting
their research to the general public.
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