First-year archaeology master's student Tomoya Kajiki describes discovering a bronze mirror at an ancient tomb in Okayama. (Michiko Nakayama)

OKAYAMA--Archaeology students have discovered an ancient bronze mirror from an undisturbed tomb from the early Kofun period (late third to fourth centuries) here in western Japan.

“I was a little freaked out when I saw the greenish thing and realized it could be a mirror,” said first-year master's student Tomoya Kajiki, 23, recalling the moment of discovery. “So much so I almost pretended not seeing it.

“When soil was removed carefully, a mirror in a tidy condition appeared.”

Okayama University’s archaeological research lab announced March 14 that the mirror, about 14 centimeters in diameter but broken in half, was spotted by the group of master students on March 11 when they were working at one of two stone burial chambers at the Tsukura burial mound in the city’s Kita Ward.

The researchers have been conducting excavation work at the mound since 2015, and it had never been previously opened by grave robbers.

The artifacts were found exactly how they were originally buried, providing important information about ancient burial customs and rituals.

It is hoped studying the tomb will help unravel the mysteries of the ancient Kibi kingdom that existed in the area, covering much of today’s Okayama Prefecture and the eastern parts of Hiroshima Prefecture.

The mirror is probably of the“daryukyo” type, one that holds reliefs of imaginary beasts holding sticks in their mouths, according to Jun Mitsumoto, associated professor of archaeology at Okayama University. Daryukyo mirrors were made in Japan.

Only 71 daryukyo had been discovered in Japan before this one was unearthed. It is the fourth in the prefecture, but the first found in its original position in the tomb.

The mirror was removed from the excavation site March 14, and it will be cleaned for further study.

Mitsumoto said the mirror will provide a big clue in dating the tomb.

“I think we can narrow down a highly accurate date of burial together with the shape of the tomb and other artifacts excavated from here,” said Mitsumoto.