How do we know where to dig?

There are many ways of discovering the presence of archaeological remains without excavation, and these should be explored first and can be used to inform a Project Design for a later dig.

These approaches are called non-intrusive techniques, as they do not involve the destruction of the archaeology. They can be applied at a landscape scale or at a site level. Non-intrusive techniques give us a broad insight in to the development of the landscape, and can unlock stories that help us understand how people interacted with it in the past. The techniques chosen often form a ‘nested’ programme of works, each stage informing the next.

The main non-intrusive investigation techniques include:

• desktop survey: the examination of standard archives and published references (such as National Record of the Historic Environment (NRHE), Historic Environment Record (HER), journal articles and site reports, air photographs, historic maps etc.)

• airborne remote sensing: the interpretation and mapping of archaeology visible on aerial photographs and from airborne laser scanning (usually called lidar). This technique brings together information on buried features revealed as cropmarks, soilmarks or parchmarks, and features visible on the surface (such as earthworks and structures).

• analytical earthwork survey: the accurate mapping and analysis of archaeological features visible above ground. This technique is good at providing detailed information on form and condition of earthwork remains, and identifying chronological relationships between features.

• geophysical survey: this can identify buried archaeological remains. A number of techniques can be used (such as magnetometry, resistivity and ground penetrating radar) each measuring different physical properties of the ground, and it is important to choose the right combination of methods for the site being investigated.

• Surface artefact mapping (fieldwalking): the collection and mapping of artefacts from the ground’s surface and the study of their distribution patterns. This technique is effective where the ground has been turned over, such as areas in arable production.

Information from non-intrusive survey and investigation is vital when considering where to target excavation. It can reveal the presence of sites and monuments not visible to the archaeologist on the ground, and can provide new interpretations of known sites. Insights gained from non-intrusive survey can also identify gaps in understanding, and help define research questions that can be addressed through excavation.

It is essential to consider which non-intrusive technique would be most applicable to the site or area of landscape to be investigated. The value of each non-intrusive method depends on a range of variables; these include land-use, geology, climate, scale, budget, time constraints, and the aims and objectives of the project. No single technique can supply all the answers. A combination of non-intrusive methods is often the best approach when considering where to excavate.

It is only after work such as this has been completed that we can properly plan an archaeological excavation – if, that is, we feel the aims of the project have not already been fulfilled by the non-intrusive surveys!

1. What are the main differences between the various non-intrusive survey techniques?
2. What order would you use the different techniques in?
3. What landscapes are most appropriate to the different techniques?
4. How do these non-intrusive techniques compare to archaeological excavation?

Share your thoughts below.