URUMA, Okinawa Prefecture--Ancient Roman coins have been discovered in Japan for the first time at the ruins of Katsuren Castle here, where they are thought to have arrived via the maritime trade in the 14th to 15th centuries with other parts of Asia.

Ten copper coins were excavated at the site, the city education board announced Sept. 26.

“This significant discovery will contribute to the study of world history including west Asia and the West,” said a city education board official.

Four of the coins, which bear what appear to be the faces of Roman emperors and Roman letters, are believed to have been minted in the fourth century.

The ancient coins, which measure from 1.6 to 2 centimeters in diameter, were found at a geological layer dating to the 14th to 15th centuries, which also contains Chinese ceramics.

One of the other pieces, found in another geological layer, bears Arabic letters and is believed to be an Ottoman Empire coin likely made in the 17th century. Five other coins are under analysis.

Registered as a UNESCO World Heritage site in 2000, Katsuren Castle was built around the 12th to 13th centuries.

The maritime intermediate trade thrived in Okinawa from the 14th to the 16th centuries, when the Kingdom of Ryukyu traded with China and realms in Southeast Asia.

“People involved with Katsuren Castle might have obtained these coins somewhere in Asia that had contact with the West,” said the education board official.

They added that the Ottoman coin was likely to have been brought to Okinawa a long time after the Roman coins in the haul.

Yasuhiro Yokkaichi, a researcher at Waseda University’s Institute for Central Eurasian History and Culture, urged a cautious stance on the discovery.

“Roman coins were also found in Southeast Asia, so the coins are likely to have arrived in Okinawa through trading with Southeast Asia," he said. "I want those who conduct an investigation of this discovery to closely examine different possibilities including that the coins came to be mixed in after much time had passed.”