Since its emergence as a science, archaeology has wrestled with a paradox: discovery involves destruction, and investigation requires intrusion. An archaeological dig cannot be undone. Once a layer has been stripped away, any information not recorded is lost. Most archaeologists have had the experience of trying to discover something new about a site that has been completely excavated, only to find that the question they wanted to ask had not occurred to the original diggers.

So knowing what lies beneath the surface before the trowel hits the soil has long been the dream of many an archaeologist. As well as saving time in determining where to dig, it would enable archaeologists to answer questions with a minimum of destruction—and potentially none at all. This dream is slowly becoming a reality, as a result of improvements in non-destructive surveying techniques. Archaeology has never been a wealthy discipline, but by borrowing tools developed for more well-endowed professions, archaeologists are developing X-ray vision—or, to be precise, infra-red, microwave and magnetic vision, which are even better.

Such tools enable archaeologists to identify and target small areas of interest, and to move away from the complete excavation of sites towards a more selective approach…...