A term used to describe a feature created by the robbing of its original filling material. In areas where stone or other building materials are scarce, or where a new structure is being built near one which is out of use, a monument's building materials may be plundered. The trench left is usually backfilled by the laborers who have 'robbed' out a wall either completely or of its facing stone. The trenches where the walls once stood and where the stone has been removed are called robber trenches or ghost walls. Archaeologists should be able to reconstruct a plan of the original structure from careful examination and recording of the robber trenches.