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.

Archaeological excavation were performed in 1981, 1987, 1990, and 2010, indicating that it was made from the end of the 6th century to the beginning of the 7th century AD, making it the last of the keyhole-shaped tumuli to have been built in this cluster.

A grey Sue ware jar was found in an excavation of the moat, instead of the usual haniwa.

Although analysis showed that it was made at a kiln in Yorii, Saitama about 30 kilometers away, no other examples have been found in the Kantō region, although similar jars have been found at the Asahi Tenjinyama Kofun in Hita, Oita and at the Fushiiwasato No.

Media related to Nakanoyama Kofun at Wikimedia Commons