Archaeologists say this bronze ring unearthed at the Shimomagari site, seen here May 16 in Ritto, Shiga Prefecture, could be a balance scale weight. (Jiro Tsutsui)

RITTO, Shiga Prefecture--It took 20 years, but archaeologists reckon they now know the purpose of a bronze ring unearthed at an ancient site here: as a weight for measuring commodities.

That, in itself, may not sound exceptional, but researchers are excited because bronze ring weights have only previously been found as burial accessories in centuries-old tombs in China and the Korean Peninsula.

The artifact was found in 1999 during excavation work of a dry riverbed that flowed during the late Yayoi Pottery Culture period (300 B.C.-A.D. 300). The dig by the municipal education board also turned up earthenware fragments and bronze arrowheads.

Officials said May 23 that the find at the Shimomagari archaeological site in this western city is likely a ring weight dating to the latter half of the second century.

Until now, the artifact had simply been described as a “copper ring” as no one knew what it was.

Bronze ring weights have been found as burial accessories in ancient tombs in China and Korea, but not in Japan.

Researchers said the discovery offered "major implications" for understanding how weights and measuring systems made their way to Japan.

The artifact measures 12.7 centimeters across, is 0.7 cm thick and weighs 89.30 grams.

Last year, Ryo Wauchi, then a research fellow with Fukuoka University, examined the ring from the Shimomagari site to compare it with the weights of four rings found in the Daho-ri Tomb No. 1 in the southern part of South Korea.

Wauchi currently works for the municipal education board of Ureshino in Saga Prefecture.

Wauchi said he found the weights of the rings from the Daho-ri Tomb No. 1 indicated the presence of a minimum mass unit that lies somewhere between 5.45 grams and 5.64 grams, whereas the ring from the Shimomagari site is roughly 16 times as heavy.

Balance scale weights from that period in history are known to increase by a power of two. Thus, weights increase by two, four, eight or 16 times.

Wauchi said he believes the ring from the Shimomagari site could be a ring weight, partly because one of its sides is flat, which would make it easy, for example, when rings are laid one on top of another.

The Shimomagari site also bore traces of bronze manufacturing as well as interactions with broad geographical areas, including Japan’s Hokuriku and Tokai regions.

It is believed the ring was brought from China or the Korean Peninsula and was used to measure raw material for bronzeware and to weigh vermilion, which was precious at that time.

“Chinese bronze mirrors from the Earlier Han period (202 B.C.-A.D. 8) have been unearthed at the Daho-ri and Shimomagari sites, which indicates interactions with China,” said Tomoyuki Nakao, a senior curator and archaeologist with the Museum of Yayoi Culture of the Osaka prefectural government. “It appears likely the ring weight was brought in as part of those interactions.”

The artifact is on display through July 15 at the city's Ritto History Museum.