Features and Structure of the Burial Mound
Yata Ōtsuka Kofun is a circular mound measuring approximately 54 meters in diameter and 7 meters in height. It is believed to have been constructed in the latter half of the 6th century. Inside the mound is a monumental horizontal stone burial chamber measuring 19.1 meters in total length, with its entrance facing southeast. The chamber consists of an entrance passage and an inner burial chamber. A single enormous stone, known as a mirror stone, forms the rear wall of the inner chamber.
The inner chamber measures 8.4 meters long, 3 meters wide, and 3.8 meters high, with a ceiling constructed from four massive stones. Three composite stone coffins are arranged along the rear and western walls. These coffins were made from fossiliferous limestone, highlighting the impressive scale and sophisticated construction of the burial complex.
Archaeological Surveys and Excavated Artifacts
A field investigation conducted in 1901 uncovered numerous burial goods. These included the pommel of a single-phoenix ring-pommeled sword, now designated an Important Cultural Property of Kurashiki City, as well as horse fittings, beads and other ornaments, Sue ware pottery, and Haji ware pottery.
In 1981, researchers carried out detailed measurements of the stone chamber. A survey of the mound and an investigation to establish its boundaries followed in 1983. These studies confirmed that the mound is approximately 54 meters in diameter and circular in shape, including its surrounding moat.
One of Okayama’s Three Great Megalithic Burial Mounds
Yata Ōtsuka Kofun is one of Okayama Prefecture’s Three Great Megalithic Burial Mounds, alongside Musa Ōtsuka Kofun in Okayama City and Kōmoritsuka Kofun in Sōja City. Although it was built in the latter half of the 6th century, additional burials are believed to have taken place until the beginning of the 7th century.
The mound is also thought to have been the tomb of the Shimotsumichi clan, whose ancestors were said to be descendants of a nephew of Prince Kibitsuhiko. The site is considered important for understanding the connections between powerful local clans in the ancient Kibi region and the Yamato royal authority.
Cultural Heritage Designation
Yata Ōtsuka Kofun was designated a National Historic Site on December 17, 1929. The designated area was expanded in 1992. In 2020, the excavated sword pommel known as the single-phoenix ring-pommeled sword pommel was designated an Important Cultural Property of Kurashiki City.
Artifacts and Related Sites
Some of the burial goods excavated from Yata Ōtsuka Kofun are held by the Tokyo National Museum in Taitō, Tokyo, while others are preserved at Kibiji Temple in Yata, Mabi Town, Kurashiki City. These artifacts provide valuable evidence for understanding the culture, social hierarchy, and power structures of the ancient Kibi region during the Kofun period.
A Legacy of Ancient Kibi
Yata Ōtsuka Kofun is a large circular burial mound built at the edge of a hill north of the Oda River in southern Okayama Prefecture. It remains an important site for archaeological research and the study of the region’s ancient history. Carefully protected as a cultural heritage site, the mound offers visitors a tangible connection to the people and society that flourished in Kibi more than 1,400 years ago.