Mendori Nagayama Burial Mound is believed to be the gravesite of a chieftain. It was built around the early 5th century in the middle of the Kofun Period. The burial mound is a scallop-shaped (keyhole-shaped) tomb that is 90.5 m long. Imagine the keyhole shape of the burial mound. There is a terrace on the east and west sides of the back circular area. The burial mound is built in two tiers with stones covering the sloping sides. Cylindrical clay figures surround the burial mound, and on the flat surface found towards the top of the mound, these figures are laid about. Clay figures shaped like a house and armor have been placed on the top of the back circular area.
A boat-shape-coffin made of shakudani stone with triangular and circular design engravings on the lid of the coffin was placed in the mound. It was robbed, but luckily, some burial accessories such as an iron sword; iron batons; iron spears; stone arrowheads; decorative pommels for swords; stone bracelet fragments in kuwagata-shape and wheel-shape; comma-shaped beads; cylindrical beads; and jujube-shaped beads were found.