A Short Guide to Archaeological Investigation
The Initial Investigation
When archaeologists are called in to investigate a site they will usually start by conducting what is called a "desktop" survey of all the evidence already available for the area before considering whether to carry out any further investigation such as excavation.
The desktop survey will involve an analysis of all existing evidence for the site. This might include:
- written sources such as maps or historical documents relating to the area
- a study of aerial photographs which might reveal evidence of previous occupation of the site through crop marks or earthworks,
- records of previous archaeological work carried out on or near the site such as field walking, earthwork surveys or excavations
- a study of artefacts already found on the site through chance finds or trial excavations.
Much of this information will be contained in the County Sites and Monuments Record. This is an archaeological database that records through a map based system all archaeological information already known about a site or in Local Studies or Record Office collections.
Once this survey has been undertaken, it might be considered advisable to carry out a number of investigations of the site using techniques such as geophysics, field walking or earthwork survey, or it might be decided to carry out some trial trenching (an initial excavation of a small part of the site) in order to evaluate just what archaeological remains might survive on the site.
A large scale excavation of an area is usually only undertaken if the site is threatened with destruction e.g. through development for housing or road building and the archaeological remains are likely to be lost. Since the introduction of PPG16 (Planning Policy Guidance Note 16) in the early 1990s, the preferred option for archaeological remains is to attempt to preserve them in situ - since excavation of a site is really only a controlled destruction of it. In reality of course, this is not always feasible and the only option is then to ensure that a full record of a site's archaeology is made before it is destroyed.
Excavation of the site is normally undertaken by professional archaeological contractors who will develop an excavation strategy based on the preliminary desktop investigations of the site. This will determine the areas to be excavated, and the main priorities in recording. It is unlikely that all of the site can been recorded in the same depth and the samples taken from ditches and pits may reveal the seeds, pollen, small animal bones and snail shells that indicate the past environment.
What is excavated on site can be roughly divided into two categories - the features (buildings, pits, roads, kilns .) and the finds or artefacts that are made within excavated features or in a non-context (i.e. not associated with a feature) location.
At Sandy the type of features excavated included:
- the stone and timber town houses, the metalworking hearths, the human burials, rubbish pits
and the type of finds or artefacts recovered included:
- pottery, coins, bronze brooches, animal bone .
Once revealed, all features will need to be recorded using scale plans and site photographs before they can be completely removed. The archaeologists will also be looking closely at how different features are related to each other - are they of the same or different date. The way the features on a site are deposited and their interrelationship is called the site stratigraphy.
The excavation and lifting of finds depends upon their material - obviously some materials will need special conservation and treatment to ensure their preservation - e.g. waterlogged organic material such as wood or leather.
All the finds will need to be cleaned and treated before work can begin on identification and analysis.
Post - Excavation
Once the excavation work is over, the task of analysing the evidence begins. Much work on particular artefacts or scientific investigations such as dendrochronology (wood dating) or radiocarbon dating may be undertaken and specialists may be asked to analyse specific materials such as the pottery or worked bone.
It is not until post fieldwork analysis has been completed that an attempt can be made to interpret the evidence from the site. Finds analysis and site records can be combined to draw out a picture of the what the site was like in the past.
Finally, once this interpretation has been made, the information has to be made available to others - from academics to the general public, the interested local resident to the schoolchild.
Peter L Drewett, 1999 Field Archaeology: An Introduction University College London UK
Kevin Greene, 1996 Archaeology: An Introduction Batsford (3rd ed)
Philip Barker, 1993 Techniques of archaeological Excavation Batsford