The coins date from ancient Rome and from the Magna Graecia period, which refers to the Greek colonisation of southern Italy from the 5th to the 8th century AD.
The Carabinieri said the coins are of considerable archaeological/numismatic interest and have an estimated market value of 3.5 million euros (3.9 million dollars).
The illegal trade was managed by a pensioner from Castelvetrano, Sicily, who sold it online after collecting them, restoring them, cleaning them and cataloguing them in a clandestine home lab.
Police got to him via regular monitoring activities of eBay auctions, the Carabinieri said.
The man was charged with trading in stolen goods and risks a jail term from two to eight years.
The total number of 7,905 coins was retrieved after further investigations and searches in Sicily and other Italian regions, a Carabinieri spokesman said.
This led to charges being pressed against 22 more suspects linked in various ways in the illegal trade, and to the seizure of 265 other stolen archaeological artefacts, including jewels and pottery.