The tumulus was believed for centuries to be a natural hill, although there was a local tradition that it contained a cave.

In 1994, further investigation using ground penetrating radar indicated the presence of a large stone structure near the top of the mound, raising the possibility that this was indeed a burial tumulus.

The innermost room contained two human skeletons, and artifacts resembling "rusty nails".

A complete archaeological excavation was conducted from May 2003, in which the hill was confirmed to be a three-tier Joenkahofun [ja] (上円下方墳), with two square base tiers and an upper dome.

[2] As the tomb had been opened in the Meiji period, and possibly earlier, there were few grave goods; however, artifacts recovered included one silver inlaid sheath with metal fittings, six glass beads, three iron swords, and about 300 iron nails.