Bulgarian police have confiscated hundreds of valuable ancient Greek and Roman artefacts during an operation targeting an organized criminal group, the Interior Ministry in Sofia said on Thursday.

About 800 items of archaeological interest including ancient coins, two mediaeval seals and a cross worn on the chest have been confiscated from six people in Montana Region, in northwestern Bulgaria, and Haskovo Region, in the south.

A marble tombstone of a Roman cavalry officer who had lived in Castra ad Montanesium, a fortified Roman camp in northwestern outskirts of today’s Montana, is also among the confiscated items.

Experts say this is only the second such tombstone found in Montana and it is particulary valuable because the inscription on its face is very well preserved.

The criminal group has been operating a channel for trafficking archaeological artefacts discovered in Bulgaria, the Interior Ministry said in a statement

One of Bulgaria’s leading dealers in illicit trading in ancient artefacts has been arrested in the course of the operation that took place on October 7 and 8, according to the statement. The name was not disclosed.