Diver discovers one of the greatest treasures of the Roman Empire

This story began in shallow water off northeastern Sardinia near the town of Arzachena, when a recreational diver saw something shine. Instead of a piece of trash, the glint came from a cluster of ancient Roman bronze coins lying just beyond the beach.

An early analysis based on the total weight suggests between 30,000 and 50,000 fourth century AD coins. For archaeologists, that mound of metal is less a jackpot and more a record of how ships, people, and power moved across the Mediterranean.

Roman coins on the seafloor

The diver reported the discovery as soon as he reached shore. Specialists from Sardinia and national cultural heritage units then arrived with police divers and underwater archaeologists to map the area and secure it.

The investigation is being coordinated by the Italian Ministry of Culture, which oversees underwater archaeology in these waters.

Its teams focus on recording fragile sites in detail, then recovering and conserving artifacts before waves, storms, or boat traffic disturb them.

On the seabed, the coins lie in two broad patches of sand between the beach and a dense band of seagrass. Many pieces remain partly buried, with only raised rims and worn edges visible above the grains.

The sandy gap is bordered by meadows of Posidonia oceanica, a Mediterranean seagrass species that forms thick underwater lawns and stabilizes the seabed. 

That setting makes it likely that a Roman ship broke apart nearby and that its remaining cargo now rests under the plants and sediment.

Coins with a Roman emperor’s face

Most of the coins are follis, bronze pieces used for everyday payments by Roman soldiers and civilians. They were low value workhorse coins rather than rare pieces reserved only for the imperial court.

A follis is a silver washed bronze coin introduced in the late third century. For scale, a famous fourth century coin hoard near Seaton in Devon, England, held 22,888 copper alloy coins.

Specialists in numismatics, the study of coins as historical evidence, have tied the hoard to the years between AD 324 and 340.

The coins include issues of Constantine the Great and his relatives and the absence of later bronze types supports that narrow time window.

By decoding the mint marks, tiny letters that name where each coin was produced, researchers see money from every active workshop of that period.

Only a few mints in cities such as Antioch, Alexandria, and Carthage are missing, which points to a ship on a long trade route.

Seagrass as an underwater archive

The coins did not rest alone on bare rock. Divers also recorded broken walls from amphorae – tall ceramic jars used to carry ship cargoes such as oil, wine, or grain.

One scientific study shows that dense seagrass meadows can trap sediments and shield buried artifacts from oxygen.

Under the right conditions, those underwater meadows build up layers that preserve shipwrecks and cargo for centuries.

The Sardinian hoard sits where the sandy bottom meets one of these meadows, which helps explain why so many coins and potsherds stayed together.

The same natural processes that protect fish and stabilize the coast are also protecting this archive of Roman trade.

Modern ecological work has also shown that underwater Mediterranean seagrass meadows are under heavy pressure from anchors, trawling, and pollution. 

Damage to those meadows does not just harm marine life, it can also expose long buried archaeological sites to waves and currents.

Piecing together a lost voyage

Each bronze disc carries a portrait, a name, and a short message about victory, virtue, or empire. When viewed together, the coins form a detailed snapshot of who held power as Constantine and his heirs reshaped politics and religion across the Roman world.

Conservators report that almost every coin recovered so far is in a remarkably legible state, with only four damaged examples that remain readable under magnification.

That condition suggests that the hoard sank quickly into a protective layer of sand and seagrass before heavy corrosion began.

Amphora fragments from African and eastern workshops, combined with the wide range of mints represented, point to a ship that probably carried everyday cargo rather than royal treasure. 

For historians, that sort of routine shipment often reveals more about daily life than a chest of gold because it tracks how supplies and wages moved to distant garrisons and towns.

As specialists catalog inscriptions and analyze metal composition, they can test ideas about inflation, military logistics, and regional trade connections in the later Roman Empire. These patterns will help confirm or challenge written sources that describe the same years.

Saving history beneath the waves

Work at the site now proceeds in careful stages. Divers map every visible coin and sherd in place, then lift them in small groups in seawater filled containers so that sudden changes in temperature or salt level do not crack the metal.

In the lab, conservators slowly remove salt, stabilize corrosion, and photograph and weigh every item before long term storage.

As results appear, archaeologists hope to reconstruct the ship-route and what the cargo reveals about broader Roman trade patterns.

According to Luigi La Rocca, a general director of archaeology of fine arts and landscape for the Sardinian region this is one of the most important discoveries of numismatic finds in recent years.

Some of the coins will likely move to regional museums once conservation is complete, while others will stay in study collections for detailed analysis. 

Together they capture a moment when one ship, one cargo, and one unlucky day off Sardinia created a dense record for future science.

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