The group consists of five tumuli, four of which were collectively designated a National Historic Site of Japan in 1992.

[1] The Miidani Kofun cluster is located in the center of the Tajima region, on a hill on the left bank of the lower reaches of the Yagi River, at an elevation of 83 to 93 meters.

[2] The No.1 tumulus is located further to the west, and is not part of the National Historic Site designation.

Of especial note was an iron sword recovered from the No.2 tumulus, which an X-ray analysis at the Nara National Research Institute for Cultural Properties revealed had a Chinese calendar dated copper-inlay inscription corresponding to 608 AD.

The site is now a public park, and is located about 13 minutes by car from Yōka Station on the JR West San'in Main Line.