Nagayama Kofun, Keyhole-shaped burial mound in Sakai-ku, Sakai, Japan

Nagayama Kofun is a keyhole-shaped mounded tomb in the Mozu group, with its square front facing south. It measures 100 m long, with a 63 m diameter rear round mound and a 68.5 m wide front section, both about 10.3 m high. A projecting terrace with fukiishi stone facing and haniwa stands at the western constriction, and a moat surrounds the mound.

Nagayama Kofun was likely built in the first half of the 5th century and is considered older than the adjacent Daisenryo Kofun (Nintoku-tenno-ryo). Although the Imperial Household Agency manages it as a baizuka of that tomb, its size and form suggest it was an independent kofun. In the Edo period it was called Nagayama-zuka or Nagayama, and traditions linked it to the graves of Wani and Yamato Takeru.

This site belongs to the Mozu-Furuichi Kofun complex, where early Japanese leaders were honored through monumental earthen constructions. The shape and scale of these burial mounds directly reflected the power and rank of those interred within.

Nagayama Kofun lies about 50 metres north-west of the Daisenryo Kofun mound, in the Higashi-Nagayamaen district of Sakai-ku. The Osaka Central Ring Route (Osaka Prefectural Route 2) runs along the south side of its surrounding moat, crossing part of it. The mound is managed by the Imperial Household Agency as a subsidiary tomb of Emperor Nintoku's mausoleum, so access to the burial mound itself is restricted; the moat and mound edge are viewed from outside.

Although the Imperial Household Agency manages Nagayama Kofun as a subsidiary tomb of Emperor Nintoku's mausoleum, its size and keyhole form lead scholars to consider it an independent kofun, likely built before the adjacent Daisenryo Kofun. In the Edo period it was called Nagayama-zuka or Nagayama, and traditions linked it to the graves of Wani and Yamato Takeru.