Where to Dig

The location of trenches is crucial to the success of the excavation. It is rare for archaeologists to intend to dig 100% of a site, even if it faces total destruction from development afterwards. Archaeologists have to decide which parts of a site to concentrate on in order to retrieve maximum information within the available time and finances.

A number of objectives will be set for the excavation, perhaps investigating features which have been revealed in pre-excavation survey, perhaps to gain an understanding of the date or ground-plan of the structures present, or possibly to excavate a certain proportion of each major deposit or chronological phase. These objectives will inform the decision on the number and size of the excavation trenches. Trenches are often positioned where as many objectives as possible can be tackled in one place: such as a point where a later building is built over an earlier building, or where two ditches or walls cross each other.

A regular, or possibly deliberately random proportion of the archaeology may be investigated on the assumption that it will provide a representative picture of the whole site: this is called 'sampling'. There are many kinds of sampling strategy, but the one factor they all have in common is that they are designed to achieve maximum information across the site from each excavated area. Some archaeologists prefer to have a flexible and informal sampling strategy so they can respond pragmatically to new information and interpretation during their field project. Others prefer to have an explicit and pre-formulated strategy so they can be sure they have investigated certain proportions of the available area and deposits.

Excavation takes place within trenches or areas. These are located within a site survey 'grid' so that every point on the excavation site can be given a horizontal co-ordinate. A benchmark is established from which vertical measurements can be taken. These are important because recording the locations of structures and finds, in both vertical and horizontal dimensions, is an essential aspect of excavation. Trenches range in size from 1 metre square test pits and slightly larger evaluation trenches giving a 'glimpse' of the archaeology in the ground, to sections of individual settlements, burial areas or ditch systems. On very large excavations, such as those required before major developments like new towns, airports or motorways, there are open areas of many hundreds or even thousands of square metres, covering multi-period archaeological landscapes of settlement, agriculture and industry.