A mound found adjoining the southeast side of Kengoshizuka in Koshi, Asuka Village. Nara Prefecture's heritage database states that this matches the Nihon Shoki's record and considers it highly probable that the two mounds are Empress Saimei's mausoleum.
Finds & research
Monolithic side-entry chamber of quartz diorite; lacquer-film fragments, iron objects and other finds.
Official status & archaeological view
Official status
Part of the National Historic Site "Kengoshizuka & Koshitsuka-Gomon Kofun" (1923; this mound added and the site renamed in 2014).
Archaeological view
The mound is levelled and its measured size is unknown, though an Asuka Village study suggests a possible reconstruction as a square mound about 20m on each side, while Nara Prefecture's heritage database considers it a square mound of about 10m per side. Its megalithic side-entry chamber of quartz diorite — hollowed out of a huge block and opening to the south — was found in 2010. It was built in the late 7th century. Nara Prefecture's heritage database states that its discovery adjoining the southeast side of Kengoshizuka↗ matches the Nihon Shoki's record for the second month of the sixth year of Emperor Tenji that Princess Ota (daughter of Emperor Tenji) was buried before the Ochi-no-Okanoe Mausoleum of Empress Saimei and Princess Hashihito, and considers it highly probable that the two mounds correspond to that mausoleum.
Field notes
Maintained with Kengoshizuka↗; free to walk through, with the chamber viewed through a fence and paid reserved openings. The list of 19 components of the World Heritage site "Ancient Capitals of Asuka and Fujiwara", inscribed in 2026, names Kengoshizuka but does not separately list Koshitsuka-Gomon.