The Hachimanyama Kofun is located almost parallel to the right bank of the Hirose River, and is orientated facing southeast.

It can be dated to the latter half of the 4th century AD due to a layer of pumice ash that was deposited by an eruption of Mount Asama found under the tumulus.

The surface was originally covered in fukiishi, some of which towards the bottom of the mound are unusually large.

Although the detailed structure of the mound has not been investigated yet, it is believed to have a gravel-lined burial chamber.

Due to finds in ongoing investigations, the area covered by the National Historic Site designation was extended in 1980, again in 2003, and again in 2020.