Jean-David Desforges, head of the French association HAPPAH (Stop the Pillage of Archeological and Historical Heritage), told a conference that many objects, especially from ancient Gaul or Nazi artefacts from World War II, were illegally dug up and sold by thousands of prospectors using metal detectors.
"In the past few years, the illegal sale of objects has exploded on the Internet," he said, despite legislation protecting buried heritage.
HAPPAH, which is endorsed by France's culture ministry, has signed deals with eBay France to alert it to suspect objects put up for sale online, something it does 1,000 times a day, Desforges said.
Desforges said he would also like to end the unregulated sale of metal detectors "as is already the case in Spain and Portugal."
Among the most important treaures last year was "an item of gold jewelry, probably dating from the end of the Bronze Age" which was found in a wood in South western France and sold on internet, causing considerable concern in archeological circles.