A diver who spotted something metallic not far from Sardinia’s coast has led to the discovery of tens of thousands of ancient bronze coins.Italy’s culture ministry said Saturday that the diver alerted authorities, who sent divers assigned to an art protection squad along with others from the ministry’s undersea archaeology department.

The coins dating from the first half of the fourth century were found in sea grass, not far from the northeast shore of the Mediterranean island. The ministry didn’t say exactly when the first diver caught a glimpse of something metallic just off shore Sardinia, not far from the town of Arzachena.