east wall, and ceiling, and two on the west wall. Inside was a Sue ware ceramic coffin shaped like a house and a wooden coffin. Although the burial chamber had been robbed in antiquity, a number of grave goods were found, including a pair of dragon hilt swords, arrowheads, and arrowhead-shaped gilt bronze products and both Sue ware and Haji ware pottery. The excavated hilt swords are an important cultural property designated by Okayama Prefecture. The tumulus is estimated to have been built around the end of the Kofun period around the latter half of the 7th century. Although it is not clear who was buried, there is a theory that he was Prince Ishikawa no Okimi, who died in 672, who played a role in the Jinshin War and was recognized as ruler of Kibi around this time. Sada No.4 Kofun The Sada No.4 Kofun was excavated in 2006. Measuring approximately 6.6 meters from north to south and 8.2 meters from east to west, it is a three-tiered square tumulus. No relics have been found in the stone chamber, but plate-shaped iron products have been excavated from the southern end of the research area. It is estimated to have been built between the end of the 7th century and the beginning of the 8th century, the end of the Kofun period, making it the newest and smallest burial mound in the cluster. Sada No.5 Kofun The Sada No.5 Kofun was also excavated in 2006. It is a two-tiered square burial mound measuring about 8 meters from north to south and about 10.4 meters from east to west. Sue ware was found in the burial chamber. It is estimated to have been built in the latter half of the 7th century, at the end of the Kofun period. Large chieftain tombs of the 6th century Kingdom of Kibi were built in the southern part of the Kibi region, but the northern region, which is an important transportation hub and rich in iron resources, came under Yamato political influence in the 7th century and the construction of large burial mounds in this region shows a shifting of political and economic power from the south to the north during this time. In addition, the Kodono Site, believed to be the ruins of a Nara period kanga (district headquarters) are located nearby, and it ay have some connection to this tumuli cluster. The