In archaeology, the systematic recovery of data through the exposure of buried sites and artefacts. Excavation is destructive, and is therefore accompanied by a comprehensive recording of all material found and its three-dimensional locations (its context). As much material and information as possible must be recovered from any dig. A full record of all the techniques employed in the excavation itself must also be made, so that future archaeologists will be able to evaluate the results of the work accurately.
Besides being destructive, excavation is also costly. For both these reasons, it should be used only as a last resort. It can be partial, with only a sample of the site investigated, or total. Samples are chosen either intuitively, in which case excavators investigate those areas they feel will be most productive, or statistically, in which case the sample is drawn using various statistical techniques, so as to ensure that it is representative.
An important goal of excavation is a full understanding of a site's stratigraphy; that is, the vertical layering of a site.
These layers or levels can be defined naturally (for example, soil changes), culturally (for example, different occupation levels), or arbitrarily (for example, 10 cm/4 in levels). Excavation can also be done horizontally, to uncover larger areas of a particular layer and reveal the spatial relationships between artefacts and features in that layer. This is known as open-area excavation and is used especially where single-period deposits lie close to the surface, and the time dimension is represented by lateral movement rather than by the placing of one building on top of the preceding one.
Most excavators employ a flexible combination of vertical and horizontal digging adapting to the nature of their site and the questions they are seeking to answer.