If the man, whose name has not been released by the authorities, had found the coins in Belgium, he would have had the right to keep them, but archaeological artifacts found in France are the property of the state.
Officials searched two properties in eastern France, a French customs spokeswoman told CNN.

The trek contained images. Credit: JEAN-CHRISTOPHE VERHAEGEN / AFP / AFP via Getty Images
In addition to the Roman coins, the authorities found more than 13,000 other archaeological artifacts of “exceptional quality”, according to the press release.
The trek included bracelets and necklaces made during the Bronze Age and Iron Ages, Roman and Gaul coins, and a Roman dodecahedron, of which there are only about 100 known examples.
Other objects included statues as well as belt buckles from different historical eras.

The seizure is one of the largest recoveries of looted artifacts in French history. Credit: JEAN-CHRISTOPHE VERHAEGEN / AFP / Getty Images
Officials seized a total of 27,400 “priceless” objects in one of the largest recovered looted artifacts in French history, the press release said.
Customs has completed the investigation and will pass the file to prosecutors in the coming days, a spokeswoman for the agency told CNN on Thursday.
French Finance Minister Bruno Le Maire praised the “exemplary cooperation” between the French and Belgian authorities.
“It enabled the seizure of a priceless archaeological treasure. The perpetrator could face jail time and hundreds of thousands of euros in customs fines,” he said.
“It is a clear message addressed to those who, for the benefit and selfish pleasure of a few, are depriving us of our common heritage and obliterating whole parts of our history.”
French Culture Minister Roselyne Bachelot-Narquin stressed “the importance of European cooperation in the face of criminal activity that knows no frontiers”.