The tumulus was designated a National Historic Site in 1938 and re-designated as a Special National Historic Site of Japan in 2020 as part of the Sakitama Kofun Cluster.

[1] The Maruhakayama Kofun is a circular-type [ja] (empun (円墳)) kofun with a diameter of 105 meters and height of 18.9 meters, and is thus one of the largest circular tumuli in Japan.

[2] Archaeological excavations have not been conducted and details of the burial chamber are unknown.

From 1985 to 1986, maintenance work was conducted on the top and east side of the mound, and on a portion of the moat.

In 1590, during Toyotomi Hideyoshi's campaign against the Odawara Hōjō, Ishida Mitsunari established his field headquarters on top of this tumulus, constructing a semi-circular embankment as part of the Siege of Oshi Castle, which is just visible from the top of the mound.