There are plenty of things you’d expect to find in the ruins of a 12-century Japanese castle—old religious relics, perhaps, or royal remnants. Ancient Roman coins are not one of those things, but as CNN’s Emiko Jozuka reports, that’s exactly what one archaeologist found at Katsuren Castle, a Unesco World Heritage Site in Okinawa, Japan.
The bronze and copper coins were found along with a cache of Ottoman-era currency during an excavation of the castle, which was thought to have stood between the 12th and 16th centuries. X-ray technology revealed that the Roman coins dated all the way back to 300 to 400 A.D., while the Ottoman coins were made in 1687.
This isn't the first time that ancient Roman artifacts have been found in Japan. As the AFP reported back in 2012, glass jewelry believed to have Roman origins was uncovered in a Japanese tomb.
Still, as Jozuka reports, the archaeologist who was called on to verify the find initially thought the coins were a hoax. As it turns out, they appear to be a very real sign of ancient globalization. As the AFP reports, it’s the first time such coins have ever been found in Japan, and archaeologists have no idea how they got to the castle—especially since at the time, Chinese currency was the main money used in East Asia.
Perhaps clues can be found in the lives of the people who built and once inhabited the castle. It’s one of five castles on Okinawa that are known as gusuku. At the time, Okinawa was culturally and politically separate from the rest of modern-day Japan. Family alliances grew into three kingdoms that ruled from fort-like castles, and by the early 1400s the area became known as the Ryukyu Kingdom. Known for its courtesy and expansive trade, the kingdom had close ties to China until 1609, when it was taken over by a feudal lord from Japan.
Though Japan did not officially close itself off from the Western world until the 1630s, the lord of Katsuren Castle was not known to have ties to Europe—let alone people who would bring ancient Roman coins to his castle. Excavations at Katsuren are nonetheless revealing a more complete picture of international trade at the time. Tiles and expensive pottery from China have been found there, too—perhaps the lord had a hookup through his Chinese friends. Or maybe a rich visitor simply lost them during a castle vacation. We may never know, but archaeologists intend to try to find out. In the meantime, the coins themselves are on view at the Uruma City Yonagusuku Historical Museum through November 25.