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 the archaeological objects found in France are the property of the state.
Officials searched two properties in eastern France, a French customs spokeswoman told CNN.

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

The confiscation is one of the largest recoveries of looted artifacts in French history. Credit: JEAN-CHRISTOPHE VERHAEGEN / AFP / Getty Images
Officials confiscated a total of 27,400 items of “invaluable value” in one of the largest recoveries of looted artifacts in French history, according to the press release.
The customs agency has completed the investigation and will pass the file to prosecutors in the coming days, an agency spokeswoman told CNN on Thursday.
French Finance Minister Bruno Le Maire praised the “exemplary cooperation” between the French and Belgian authorities.
“It allowed the seizure of an invaluable archaeological treasure. The offender is liable to imprisonment and hundreds of thousands of euros in customs fines,” he said.
“It’s a clear message to those who, for the benefit and selfish pleasure of a few, deprive us of our common heritage and erase entire sections of our history.”
French Culture Minister Roselyne Bachelot-Narquin stressed “the importance of European cooperation in the face of borderless criminal activity”.