300m long (7th nationally, 3rd in Mozu group). 3-tiered, with the front section rising to 25.9m — wider and taller than the rear circle, a late trait in keyhole-mound design. Sakai City and the IHA have investigated the site; Sakai City excavated the inner moat in 2012–2015. It stands at the south-eastern edge of the Mozu group, in Mozunishinocho, Kita-ku, Sakai. Constituent monument of the "Mozu-Furuichi Kofun Group" UNESCO World Heritage Site (2019). The IHA manages the mound as a reference site rather than a confirmed imperial mausoleum.
Finds & research
The mound is built in three tiers with projections on both sides of the waist. In the moat east of the rear circle, up to seven rows of postholes (max. ~12m across, some timbers surviving) are thought to mark a timber bridge once thrown over the water, and a further outer moat has been traced and preserved underground. Cylindrical haniwa set edge to edge were found on the first terrace, a large Sue ware jar on the projection, and figural haniwa plus umbrella-shaped wooden haniwa in the moat. The burial facility and grave goods remain uninvestigated.
Official status & archaeological view
Official status
According to Sakai City, the Imperial Household Agency designates and manages the mound as the "Higashimozu Ryobo Sankochi" (reference site), treating it as an empty tomb of Emperor Hanzei. A reference site is a category the IHA manages like a mausoleum because it could possibly be one; it does not establish the occupant. The inner moat around the mound was added to the National Historic Site "Mozu Kofun Group" in 2019 as the "Nisanzai Kofun inner moat".
Attribution (jitei): the Imperial Household Agency's determination of whose tomb it manages — separate from heritage designation.
Archaeological view
Occupant unconfirmed. Dated to the late 5th century, it may represent the final phase of large-scale mound construction in the Mozu group, following Daisen and Kamiishizu Misanzai. The postholes in the moat east of the rear circle run from the mound slope to the embankment and are read as the footings of a timber bridge across the moat, put up at the very end of construction or just after it and removed again after short use in the building work or the funerary rites.
Field notes
The official World Heritage site gives about a 15-minute walk southwest from Nakamozu Station (Nankai Koya Line / Osaka Metro Midosuji Line). The mound is managed by the IHA and cannot be entered; view it from the surrounding streets.