Matthew Walker discusses whether advances in archaeological surface survey techniques have made the need for excavation redundant.
Most people assume that excavation is the archaeologists main concern. Most people are wrong. Today, excavation is probably what archaeologists do the least. That is not to say that the criticality of excavation has diminished within Archaeology. It is just that operational difficulties with excavation, changes in approaches within Archaeology and advancement in technology such as improved surface survey techniques make excavation less extensively required. Yet when it is used excavation is much more intensively employed.
Originally excavation, whether unplanned, in the form of grave robbing or curiosity, or planned, in the form of a structured approach was the main way in which evidence, knowledge and understanding could be acquired. Where excavation is most often employed today is in rescue archaeology. Here, archaeologists are given a very limited amount of time to examine and rescue artefacts prior to some other construction programme, coastal erosion or perhaps a road building programme. This is due largely to the legal or planning framework and the fact that the developer more often has to pay for the work.
This essay seeks to review how changes not only in surface survey techniques but other pressures have changed the way excavation is used in archaeology today. This essay sets out to describe current concerns with excavation, analyse the modern approach to archaeology, discusses a wide range of alternative ‘surface’ exploration techniques, explores the limitations of each approach and concludes by placing excavation in the context of a 21st century approach to archaeology. It is essential to place the role of excavation within context of a broader analytical process because excavation is just another tool in the archaeological kitbag. The issues are, why it has to be used and what is it used for?
What’s wrong with excavating?
Excavation has served archaeology well and it is the public’s perception of the role of archaeology. Yet there are problems with excavation as an approach. It is after all a very destructive process. More often than not it ends up destroying part of the very evidence that needs to be examined. It is also immensely expensive. Despite volunteers excavation is highly labour intensive and therefore expensive in terms of costs such as labour, equipment, travel, measuring and monitoring equipment and accommodation. And moreover it can be very time consuming. Many sites have excavation programmes that run over decades. And for some, excavation can have legal issues in terms of access to the site, time spent on the site and ways of working. There are also examples where permission has been denied due to religious influence, such as in Japan. The excavation of burial or culturally important sites is fraught with access issues. So excavation is not without it’s difficulties. And despite advancements in new surface techniques, which are described later, the role of excavation within the research process was inevitably going to decline if only due to financial, environmental and cultural pressures.
Changes in approaches within Archaeology
What is less well understood by the general public is that there have been a number of trends which have further contributed to the diminishment of excavation as an activity. As Bahn puts it “there have been two major trends over time; first, excavation has become far slower and more painstaking…. The work is incredibly meticulous… Secondly, we are acquiring vastly increased quantities of materials and we can learn far more from what we have (1).” The conclusions to be drawn from this would appear to be contradictory. Whilst excavation is getting more expensive and thereby more difficult to undertake we are now able to do more analysis with less sampling.
As technology improves we are able to undertake a wide variety of analysis from microscopic, radio carbon dating or even DNA samples. The ability to determine more, from fewer samples again suggests that less excavation is required. Moreover, more often than not the balance of effort now rests with the specialist analysers such as pollen experts and dating analysis rather than the excavators. So, again some of the requirements for extensive excavation have diminished through the advancement of other analytical techniques and not just surface survey techniques. Simply put it would appear we don’t need to do as much excavation as we used to get the same results.
Furthermore, Archaeology itself has changed in a number of ways. No longer is the emphasis simply upon the acquisition of material culture or artefacts. In many cases, we have a reasonable understanding of the surviving material culture. Indeed, Bahn quotes examples in Egypt and Italy where items are reburied in the ground simply because the museums are too full, theft may be ripe, preservation difficult and documentation slow. In many cases further excavation would add little to our understanding and preservation in situ is the best option. So once again we can see the need for excavation as a means of acquiring material culture is declining.
Archaeology has changed in other ways. The emergence of processual archaeology under Binford and others again moved archaeology towards broader concepts of explanation, process, deduction, hypothesis testing, question setting and response. Answering questions about the organisation of societies, the environment, and the trading contacts employed, their thought processes and their diet have a much greater importance today. And answering these how and why questions implies a much broader scope of work. Excavation alone cannot answer all these questions. So for both theoretical reasons and practical reasons described above the acquisition of material culture through excavation is no longer the main driving force. This again reduces the reliance upon excavation as a primary analytical tool.
Given such a broad approach Archaeology needs a structured research process. This procedure is described by Renfrew and Bahn as research design. Research design has four components, namely; formulation, the collection and recording, processing and analysis and publication. For example, more detailed work in the formulation part can focus lines of enquiry into a specific area and thereby again reduce the amount of excavation required. As we have already mentioned more meticulous collection and recording can reduce the requirement to excavate and indeed revisiting and reinterpreting original notes can prove highly instructive. Again this reduces the requirement for extensive excavation.
As the questions currently posed by Archaeologists tend to be more ‘strategic’ the focus of the field work is also of a strategic nature. Overall landscapes, context, trading patterns and systems are more important than individual sites. As such this requires different techniques. As Greene states “field work today is rarely directed at a single site. It usually forms part of a comprehensive study of an area”. He continues ” studies are designed to elucidate the broad agricultural, economic, and social developments” (2). As Renfrew and Bahn surmise “Today archaeologists study whole regions”. They continue “the focus has broadened to take in whole landscapes and a surface survey at sites in addition to – or instead of – excavation (3).” So once more the reliance upon excavation as a primary tool is diminished.
The role of surface survey techniques
All these changes in cost, approach and technology have led to or perhaps been partially caused by a new set of archaeological tools. These tools need to be overlaid within the archaeological process. Sites can be discovered through a variety of means. These might include research on word of mouth, family history, original research, local history, place names, records of activity, register of sites and even by accident. Most often sites are known about and identified through research sources and checked by a surface visit.
Once located site analysis begins through some form of ground or surface reconnaissance. At the strategic level aerial and satellite photography and analysis is useful. Photographs have two purposes. Vertical views can provide a quick overview or mapping capability which is important for context. More sophisticated images from specialised films such as infrared, radar mapping and radiation signals can provide insights into structures and spatial networks. Photographs taken from the correct oblique angle and with the right light can highlight shadows, crop marks, buildings, tracks and other infrastructure often imperceptible or confusing on the ground. The availability of declassified photographs, the relative ease of obtaining such items and their power for analysis makes aerial study very attractive. As such aerial photography is considered one of the most important archaeological developments in the 20th century and has contributed to a number of new finds and lines of enquiry. And given archaeology’s requirement for context, aerial photographs provide a very valuable asset.
However photographs don’t provide all the answers. For example it is difficult to tell elevation, age, scale, purpose, sequence and most fundamentally it only records that which is physically visible on the surface. So we may have a good visual record of the last occupation but what of previous ones. Aerial photography needs to be assisted by other techniques.
The role of field walking
The classic surface survey technique is field walking. Field walking can be random and or sample based but invariably has some form of structure such as transects to facilitate recording. This approach can cover large areas which is useful in “regional” analysis and where evidence is likely to be more scattered due to migratory or hunter gather type activity. Field work of this type is proving immensely useful in providing the broader context and is very cost effective.
Issues remain in the ability of individuals who have varying capacity to identify objects, the impact of the natural environment on material culture and the walking resources required. As Renfrew and Bahn comment “now that surface survey has become not merely a preliminary to excavation but in some instances a substitute for it … a vigorous debate is taking place….about how far surface traces do in fact reflect distributions below ground. They continue “the relationship between surface and subsurface is undoubtedly complex ands varies from site to site and it is therefore wise to determine what really is below the ground (4)”
The role of sub-surface exploration
So how can we best explore below the surface. Whilst the purpose here is to view what is below the surface the work takes place on the surface so it has been included as a surface survey technique. There are many ways to view the sub surface. None evasive approaches can use, echo sounding, electromagnetic magnetic, metal detectors, electrical resistivity, radioactivity, thermography, geochemical analysis and even dowsing.
Sound waves such as sonar have been used to detect tombs in the Valley of the Kings and thereby avoid unnecessary exploratory excavation. And such techniques have great validity in underwater work. Probes have been employed involving rods and augers at the end of which may be attached lights and cameras. Such techniques have been used successfully by Hurst Thomas in the USA, Lerici in search of Etruscan tombs and work on the Pyramids.
Ground based radar can be used. This radar not only detects variation in the composition of the soil which might indicate filled ditches or graves but can also indicate the depth at which variation occurs. We can therefore generate three dimensional maps and time slice the soil. This can help show how many possible layers of settlement there have been. This can be hugely useful in pinpointing where to excavate or indeed whether there is any thing to excavate.
Two other techniques for non evasive surveys are use of a magnetometer and resistivity. A Magnetometer measures the magnetic properties of the soil and highlights where iron oxide concentrates are higher. Magnetometers are good for cut features and work best in pre-historic sites and were used successfully in analysing the route of the M3 motorway. By identifying the locations of postholes, for example, they can help survey and direct subsequent excavation. Generally they are an efficient way but care needs to be taken with external influences such as power lines.
Resistivity measures electrical resistance and is based on the relative electrical conduction capability of various materials. The principle benefit being that the damper the soil the less resistance it will show to an electrical current. As Renfrew and Bahn comment “this technique works particularly well for ditches and pits in chalk and gravel”(5). It is then possible to map subsurface features without any form of excavation. The technique can be slow and is best used when ditches and pits are being sought as opposed to walls. Thus it is very useful in pre-historic and not so in Roman and beyond. Again resistivity can help pinpoint areas for excavation.
Geophysics helps with detailing and focusing of subsequent work. But clearly it usually requires that a hypothesis is being tested as each technique has its own advantages and disadvantages. The appropriate use of the right geophysics tool can substantially aid an excavation strategy.
The role of Geographical Information Systems and documentation
Moreover raw material requires interpretation. This requires human skill and computer speed. Integrating interpretation with Graphical Information Systems represents a huge advance in presentation and “what if” modelling. With GIS physical, human and natural activity can be overlaid on the environment. Patterns can be established and resource requirements calculated. This helps to answer the hows and the whys of modern archaeology and again helps focus any follow up excavation work.
There is a realisation today that part of archaeology’s role is to ensure that good records and documentation is kept. This leads to robust project control processes both during the overall project and particularly during excavation. This realisation is based upon the fact that we may never be able to truly explain the past but by leaving good records of our work they are available for subsequent reinterpretation. Again as most archaeology is public funded and requires reporting and presentations the resources available for extensive excavation are again reduced. Chapman’s work at Gatas is evidence of this where sizeable progress reports are required to renew permits for the following year (6).
How is excavation used in practice?
So far we have commented up the pros and cons of a variety of survey techniques. We have stated that excavation has difficulties due to cost, time and access. Moreover these operational difficulties are compounded by the capability of other techniques to contribute much to the research process. From aerial photography to sub surface radar much can be understood without resort to excavation. A case study on the Roman town of Wroxeter quoted by Renfew and Bahn uses all these techniques (7). But only 1% of the nearly 200 acre site has been excavated.
So why do we still excavate?
Yet excavation has its advantages. “Digging” as Greene suggests ” still delivers an unmatched quality of evidence” (8). It is only through excavation that hypotheses can be tested. Moreover in response to concerns we have seen changes in the way excavation is carried out. We have seen a change in excavation techniques that reflect changes in thought. Originally most excavation was brutal and vertical. More lately increasing excavation costs and disruption concerns encouraged keyhole excavation. And today in keeping with the new approach we are seeing the increased use of area or horizontal excavation in order to provide context.
In some cases excavation is the only way we can acquire the detailed evidence of smaller objects of material culture and read the story being told by the stratigraphy. Accurate dating can be acquired and sequencing through analysis. Excavation is the only way to acquire ephemeral and environmental evidence. Excavation also helps with chronological analysis by helping to identify changes in use over time and distinguishing between different layers of development. At the Gatas site it was only excavation that help separate pre-historic buildings from much later Arabic ones. Excavation provides vertical and horizontal analysis that may otherwise over looked. So excavation is good and in many ways the final technique to turn to.
Greene concludes “proper research programmes are less exciting and more expensive than unplanned exploration, but their results allow much firmer conclusions to be reached about site distributions, settlement patterns and other features of the ancient landscape. Our ability to investigate ancient landscapes and environments, without resorting to the destructive process of digging into sites, means that no excavation work should be carried out until a programme of field work and documentary research has been completed. It is impossible to ask valid questions about an individual site without understanding its place in the historical and natural environment”(10)
Renfrew and Bahn agree “until the present century, individual sites were the main focus of archaeological attention and the only remote sensing devices were a pair of eyes and a stick. The developments of aerial photography and reconnaissance techniques have shown archaeologists that the entire landscape is of interest, while geophysical and geo-chemical methods have revolutionised our ability to detect what lies hidden beneath the soil. Excavation should be the last resort as it involves irreversible physical intervention” (11). But it may ultimately be the best technique the archaeologist currently has.
1)Bahn P, Archaeology, A very short introduction. Oxford p 12
2)Greene, K, Archaeology An Introduction (Routledge 2001) p38
3)Renfrew & Bahn, Archaeology: Theories, Methods and Practice, Thames & Hudson p 116
4)Renfrew & Bahn, Archaeology: Theories, Methods and Practice, Thames & Hudson p 92
5)Renfrew & Bahn, Archaeology: Theories, Methods and Practice, Thanes & Hudson p 99
7) Renfrew & Bahn, Archaeology: Theories, Methods and Practice, Thames & Hudson p 100
8)Greene, K, Archaeology An Introduction (Routledge 2001) p 77
10) Greene, K, Archaeology An Introduction (Routledge 2001) p 45
11)Renfrew & Bahn, Archaeology: Theories, Methods and Practice, Thames & Hudson p 116