A terminal-period octagonal mound with a two-room side-entry chamber. The adjacent Koshitsukamikado Kofun and its relationship to written accounts support an imperial-family hypothesis. It became a World Heritage component in 2026.
Finds & research
Finds include dry-lacquer coffin fragments, gilt-bronze coffin fittings, iron clamps and nails, glass beads, and teeth. The chamber has two rooms, with plaster surviving on the walls.
Two views on the occupant
Archaeological view
A late-7th-century octagonal mound at Koshi, Asuka. Asuka Village records an upper-tier diagonal of 18.5m (the lower tier spans about 22m across opposite faces) and a height of about 4m, with rammed-earth construction. Its side-entry chamber was hollowed from a huge tuff-breccia block, divided into two rooms with carved coffin platforms. Its octagonal form (reserved for terminal-period sovereigns), the two-room chamber, and the discovery right in front of it of Koshitsuka-Gomon (held to be Princess Ota's grave) matching the Nihon Shoki's note that Ota was buried "before Empress Saimei's tomb" make a joint burial of Empress Saimei (Kogyoku re-enthroned) and her daughter Princess Hashihito the leading identification, though it is not archaeologically confirmed.
Imperial Household Agency view
The IHA does not designate this mound as a mausoleum. It assigns Empress Saimei's tomb to Kurumaki-Kenno Kofun (the Ochi-no-Okanoe Mausoleum) in Takatori, so this mound stands as the stronger archaeological candidate rather than the official tomb. Asuka Village manages it as a National Historic Site, opened after restoration in 2022.
Field notes
The reconstructed mound and adjacent Koshitsukamikado Kofun are open. Check current Asuka Village guidance for fees, hours, and chamber-viewing conditions.