From Helen's most recently linked article:

The coins, dating from the first half of the fourth century AD, were found in seagrass not far from the town of Arzachena.

They were first spotted by a diver who saw something metallic out of the corner of their eye.

The diver alerted authorities, who sent divers from an art protection squad along with others from the Italian cultural ministry's undersea archaeology department.

Exactly how many coins have been retrieved has not been determined yet, as they are still being sorted.

A ministry statement estimated that there are at least about 30,000 and possibly as many as 50,000, given their collective weight.

"All the coins were in an excellent and rare state of preservation," the ministry said.

The few coins that were damaged still had legible inscriptions, it said.

"The treasure found in the waters off Arzachena represent one of the most important coin discoveries," in recent years, said Luigi La Rocca, a Sardinian archaeology department official. . . . Given the location and shape of the seabed, there could be remains of ship wreckage nearby.

That ship will be a story, if they find it!