Sites where Roman material lies buried in the ground can be identified in a variety of ways. They range from the well-known and obvious places - the major centres of the Roman world - to limited or minor sites of indefinable type, whose presence is known or surmised only by a telltale scatter of coins or pottery. As the clues to a site's existence vary, so also do the methods that the archaeologist can use to detect and assess them. The processes of deduction about the existence or the extent of Roman sites may on occasion seem little more than inspired guesswork. There is far more than this, however, to the skill of interpreting what lies under the ground, and clues as to the nature of archaeological sites can be gained from several different sources.