Amateur diver unearths 50,000 ancient 4th-century Roman coins beneath sea sand in Italy

A diver off the coast near Arzachena town in Sardinia, Italy, has uncovered a remarkable cache of fourth-century bronze coins, with initial assessments based on weight pointing to 30,000 to 50,000 pieces. The coins were found scattered across a sandy area between the beach and underwater seagrass. The team also suggested that fragments of amphorae likely came from workshops in Africa and parts of Asia, indicating trade movement through this route in late Roman times, according to a report in Earth.com.

“The treasure found in the waters off Arzachena represents one of the most important coin discoveries,” in recent years, said Luigi La Rocca, general director of Archaeology, Fine Arts and Landscape at Italy’s Ministry of Culture.

The heritage of the government led archaeology to set the tone for the discovery, finding it an exact moment in the economy and politics of the Roman world, a time when new rulers and reforms reshaped daily transactions.

Where were the coins found?

These coins were discovered off the northeastern coast of Sardinia, near present-day Arzachena. The seabed in this region forms a shallow shelf, allowing currents to disperse objects across a wide area without quickly burying them beneath layers of sediment.

Researchers identified two primary scatter zones within sandy patches framed by thick seagrass. This natural boundary is significant, as the roots of the plants stabilise the sand while still leaving coins and pottery fragments partly exposed at the surface.

Among the findings are broken amphorae, suggesting the site was linked to active trade routes across the Mediterranean. With some vessels originating from North Africa and others from the eastern provinces, the evidence indicates that merchants were combining goods from multiple regions on a single journey.

What coins tell us about money?

Most of the coins are follis, a sizeable bronze piece introduced during Diocletian’s monetary reform. The earliest examples weighed close to ten grams and were coated with a thin layer of silver, an attempt to make base metal appear more valuable.

As time passes, a signal of the pressures any empire faces while trying to fund armies, bureaucracy, and public works, the silvering and weight slipped. However, the face value of the coins kept everyday trade moving even as the metal content declined.

By the early fourth century, folles served as a common currency across the Roman Empire. A sailor settling his bill used the same denomination a farmer used inland, making hoards like this valuable for historians in tracing the circulation and reach of currency.

Though small in size, coins provide rich historical insights. Their images, inscriptions, and mint marks reveal rulers, political messages, and minting locations. Studying collections highlights broader patterns, such as links between coin surges and military or political events, or trade routes across seas.

Metal composition and corrosion layers preserve environmental traces, while striking marks shed light on ancient minting techniques and workshop practices, making coins vital tools for historical research.