When the foundations of a stone building a robber trench is left. The stone may then be reused elsewhere. The trench is then refilled, usually with the material such as mortar which cannot be reused. For the foundations to have been treated in this manner, the building above must have been removed. Therefore this archaeological feature may be the only indication a building existed on a site.
- Barker, Philip (1993). Techniques of Archaeological Excavation, third edition. London: Routledge. pp. 34–35. ISBN 0-415-15152-X.