Archaeological sites may be excavated clandestinely to obtain objects and relics for sale on the art market or to museums. Such looting of sites destroys their value as a source of information on the cultures that lived there and on the origins of the modern culture in the region. It may also destroy the importance or beauty of sites for visitors, whether foreigners or citizens of the country

Recently clandestine or illicit excavations have increased considerably and in some cases are conducted on a large scale with advanced equipment. The Four Corners area in the southwest of the USA as estimated 60-95% of some 1.5 million sites including cliff dwellings, dry caves and buried villages have been looted. Under-water thieving of historical objects has grown to considerable proportions as well

The pillaging of burials is believed to have been a reason for the construction of the pyramids. In more recent centuries, underprivileged nations have traditionally provided much of the raw material for anthropologists and archaeologists from more prosperous countries. As a result, many museums may own artefacts acquired under circumstances that were not legal or which resulted from scientific excavation. In the USA, indian artefacts are bringing high prices from private collectors; a single Mimbres Indian, a tribe extinct since the 12th century, bowl recently sold for $40,000

Willingness of private collectors, and private and public museums to purchase artefacts that lack documentation and proper export papers, provides a persisting market for thieves