Last month, two men snorkelling off Spain’s Mediterranean coast on a family vacation found a stash of Roman coins that turned out to be one of the largest of its kind ever discovered in Europe.

The gold coins date between the fourth and fifth centuries AD, Rafa Burgos reports for El Pais. Brothers-in-law Luis Lens and César Gimeno spent two hours using the corkscrew of a Swiss army knife to free eight of the pieces from a rock crevice about 20 feet underwater in Portitxol Bay.

Later they contacted the local authorities and returned with underwater archaeologists from the city of Xàbia, the University of Alicante (UA) and the Spanish Civil Guard. The team eventually recovered 53 coins, 3 nails, and lead shards that were likely once part of a chest that contained the treasure.

“It’s amazing”, says Lens El País. “It’s every child’s dream to find a treasure. “

The pieces are in such good condition that researchers were able to read inscriptions on all but one, Jack Guy reports for CNN. The Roman rulers depicted included Valentinian I (3 coins), Valentinian II (7 coins), Theodosius I (15 coins), Arcadius (17 coins) and Honorius (10 coins). The reigns of these emperors lasted from 364 to 423 CE

“It’s very important,” AU historian Jaime Molina Vidal, who led the underwater investigation, told CNN. “It’s extremely valuable.

Molina says the pieces were likely intentionally hidden rather than lost in a shipwreck. A wealthy local landowner may have hidden them to protect them from invaders. During the 5th century AD, “barbarian” groups, including the Alans, Suevi and Vandals, advanced on Hispania (now Spain and Portugal), taking advantage of the power vacuum left by the failing Western Roman Empire.

“[T]he towns were in decline and power had shifted to the great Roman villas, to the countryside, ”says Molina. El País. “To exchange [had] been eradicated and the sources of wealth [became] agriculture and animal husbandry.

According to Molina, the owner of the coins was probably not able to use them as currency in the chaotic circumstances, but wanted to preserve them for the future. The individual apparently took the coins out onto a boat and sunk them in the bay, but died before he could recover their hidden treasure.

Researchers will restore the pieces and exhibit them at the Soler Blasco Archaeological and Ethnographic Museum in Xàbia, UA notes in a statement. The Valencian government is providing around $ 21,000 for further underwater excavations in the area.