Excavation is one of the most commonly known and used techniques of archaeological investigation. It involves the systematic removal of data from the ground. Excavation provides the most complete evidence for human activity during a particular period and how these activities changed over time. There are many approaches to excavation, but at its most basic, the method involves looking at activities horizontally in space and vertically through time.
By its very nature, excavation is a destructive and costly process. It is an unrepeatable experiment that requires precise methods of data extraction and recording. Before excavating a site, it is essential to understand how sites are formed. Sites are what remains from settlements and other structures. The residues of a past social system will change over time due to decay, erosion, robbing, and the effects of plant and animal action. It is thus important to recognize these processes and distinguish them from the past actions that led to the creation of the site.
To understand this, it is essential to understand the principle of stratigraphy. This is a geological principle that states that layers of strata are laid down according to processes: The layer at the bottom is the oldest layer, while the topmost layer is the most recent. This is called the law of superposition. Understanding this process is crucial for interpretation and dating purposes.
The archaeologist, then, must carefully remove and record each layer and understand the stratigraphic sequence. He or she must be able to recognize how the process works. For example, a pit dug from a higher into a lower layer may lead to later materials being found in lower levels. Strata can also become inverted; for example, a series of strata can be eroded to the bottom of a valley. To this, one must add what Michael Schiffer calls “N-transforms,” natural processes which affect the archaeological record, for example, burrowing by animals and seismic activity. Changes brought about by humans are called “C-transforms” (cultural transforms).
The first requirement, how-ever, is identifying the survey area in which to operate. Once that is accomplished,
the archaeologist must then break down the region into smaller units in order to test the viability of any sampling strategy, particularly in little-explored areas. The major problem with this is in extrapolating whether the validity of results are representative of the survey region as a whole.
Such sampling techniques include systematic, random, and stratified random sampling. Systematic sampling can be thought of like alternating black-and-white pieces on a chessboard, which assumes that the sites themselves were laid out in a gridlike format approaching a modern city square layout. The pitfall is that the excavators may hit or miss everything if the layout of the site in question does not correspond to the idealized, superimposed excavation grid.
An alternative, random sampling uses a method whereby the sample squares in the survey region are fixed by randomly chosen coordinates. This method ignores known material culture distributions and environmental boundaries. While it might appear that such randomly chosen squares will be distributed widely, in practice, it is more common for tight clusters of squares to appear, leaving large sections of the surveyed region unsampled. Thus, this method does not take into account any knowledge of the landscape and the impact this may have had on the distribution of settlement and material culture remains.
As a result, the most commonly used sampling method is stratified random sampling. The survey area is first divided up according to its environmental or topographic layout, and sampling is then undertaken within each of the zones as deemed appropriate. This method has the advantage of combining ecological knowledge with the power of random test excavations.
However, even stratified random sampling has its problems. Although it attempts to balance statistical variability with representativeness, the region chosen for sampling is determined both by financial considerations and a degree of expectation on the part of the archaeologist about the nature and size of the site or sites expected. Therefore, the interplay between practical and theoretical considerations is a reflection of the research designs undertaken.
An example of good surveys is to be found in rock art studies. Many rock paintings are present in rocky terrain, which makes targeted surveying a necessity. Not all geological formations are suitable either for painting or for long-term survival of art, and field teams will normally focus on those geological zones that maximize the potential for mapping new occurrences of rock art sites.
The focus on the methodology of excavations is far later in the history of archaeology. Early approaches simply involved the extraction of material deemed interesting by the excavator. While many such endeavors are accompanied by accounts, these are very different from the site reports familiar to students and archaeologists. The birth of modern techniques dates to the 19th century. The British Lieutenant-General Pitt Rivers developed a precise methodology during excavations on his estate, Cranborne Chase. His meticulous attention to detail was simply groundbreaking.
Archaeological excavation methodology and its procedures are typical of sampling. Factors of preservation, together with the economics involved in setting up the research project, result in excavators adopting sampling procedures that are best targeted toward achieving the objectives of the mission.
Attention also is paid to other pragmatic considerations, like natural formation processes, as archaeological sites can have complex physical and organic environments. These include water and wind actions, animal depositions and interference, as well as plant growth. The impact of these actions could disturb the site in such a way that detailed reconstruction is required in order to interpret the original material traces in a meaningful fashion.
The reasons behind why a particular site was chosen to be excavated, and the manner in which it was, must be recorded. A test of good record keeping is replicability, which permits another archaeological mission to accurately track the steps taken by its predecessor and enables participants to access the excavation strategies employed and to reconstruct the contexts of the material culture unearthed. Although this attention to detail is important, as with all archaeological work, there is a continual interplay occurring between research aims, technical developments, and theoretical perspectives.
The interplay between cultural and natural formation processes, operating between when the site was first used and the time of excavation, potentially renders the stratigraphy of sites complicated. Repeated uses of a site by hunter-gatherers, for example, are difficult to separate out into their discrete visits. However, archaeological traces of fireplaces and food refuse are manifested through localized, subtle alterations in soil color. These are called lenses, which are present within the stratigraphic layer.
At sites that have been visited repeatedly for a lengthy period of time, it is often difficult to distinguish between the complex series of lenses and layers that develop. The archaeologist records such stratigraphies through the use of sections: the stratigraphy of a straight side in a designated trench.
In situations where there are no discernable differences in soil color or texture, the archaeologist still needs to maintain vertical control and therefore may elect not to try and excavate according to faint stratigraphic layers, but instead in arbitrary vertical units called “spits.”
Horizontal and vertical control of deposits becomes even more paramount when dealing with sites under bodies of water; indeed, this is what distinguishes archaeological research from treasure scavenging.
Excavation underwater is rendered problematic by the presence of multiple hazards not encountered on the surface: seabeds of various textures exposed to currents, depth of sediments accumulated on top of the archaeological deposit, and the quality of visibility. Grid squares, made of rope, need to be placed over the designated area of the site and secured in place by concrete sinkers. Additional sinker markers are required for assisting in laying out the quadrants, which are buoyed and mapped using theodolites from the surface.
Thus, excavation techniques vary widely and are adapted according to the research requirements and the physical nature of the site in question. Despite the differing views held by archaeologists on the nature of the interaction between theory and data, the central tenet is to accurately establish the context in which the assemblages excavated occurred.
Stratigraphy as Dating
When deciding on what form of stratigraphic units to follow in an excavation, the archaeologist is also effectively deciding on the type of chronology to employ. Different, and sometimes discrete, human actions get compacted together by soil color and texture into layers. At Stone Age sites, many hundreds of individual actions and occupations may be compacted into a layer. Thus, archaeologists are confronted with the tangle of dealing with compacted human actions through artificially dividing the actions into discrete slices.
In this way, stratigraphy is at the heart of the archaeological concept of time, enabling reconstructions of chronologies to be undertaken through relative and absolute dating techniques. Examples of relative dating include analyzing and comparing the faunal compositions of neighboring or faraway sites, constructing pottery seriation sequences, and more specialized techniques, such as contrasting the chemical composition of fossil bone material. Absolute dating techniques, providing age estimates that refer to a calendrical time scale, are based either upon radioactive decay or other natural processes.
Excavation is the most visible part of archaeology. In the public mind, it is what archaeologists do. However, as any dig participant can attest, postexcavation is a far more time-consuming and equally important activity. Excavation is not meant to stand alone; the processing and publication of material is equally important.
Moreover, it is not always possible to fund excavation projects and/or obtain legal permits. For this reason, surveys have become increasingly important, for example, in the Mediterranean. While surveys potentially offer a broad range of information in a relatively shorter space of time, excavation remains the best way to uncover and document the past.
On another level, excavation provides an excellent opportunity to create dialogue with the nonarchaeological community. Ian Hodder’s excavations at Catal Hoyuk are an example of reflexive archaeology and dialogue with various communities. Finally, the material culture recovered must be handled and conserved appropriately. Excavation also raises many contentious issues, including repatriation and claims to land rights.
- Barker, P. (1993). Techniques of archaeological excavation (3rd ed.). London and New York: Routledge.
- Hall, M. (1996). Archaeology Africa. Cape Town, South Africa: David Philip.
- Renrew, C., & Bahn, P. (2004). Archaeology: Theory, methods, and practice. London: Thames & Hudson. Roskams, S. (2001). Excavation (Cambridge Manuals in Archaeology). Cambridge: Cambridge University Press.
- Schiffer, M. B. (1996). Formation processes of the archaeological record. Salt Lake City: University of Utah Press.