A terminal-period octagonal mound in Hirata, Asuka Village, ~200m north of Takamatsuzuka Kofun (id:264). Built in the early 8th century as one of the earliest cremation burials of sovereign rank. The octagonal plan was reserved for 7th-century emperors; despite its small size, it is of exceptional scholarly value as a royal tomb from the dawn of cremation in Japan. Located in Asuka National Government Park with free access to the mound. Inscribed in July 2026 as a component of the UNESCO World Heritage site "Ancient Capitals of Asuka and Fujiwara."
Finds & research
Corridor-type stone chamber (ten dressed stones, nine surviving; ~90cm square interior fully coated with vermilion). Sue ware and a shoe-shaped stone object recovered. The cremation urn was lost to medieval looting; one theory identifies it with a gilt-bronze four-ringed jar in the Imperial Collections.
Two views on the occupant
Archaeological view
An octagonal mound (~19.5m across opposing sides, three tiers) surrounded by three concentric stone pavements (outermost ~32.5m across). The 2020 survey by Asuka Village and Kansai University confirmed the structure. The burial facility is a small corridor-type stone chamber of dressed tuff and granite, only ~90cm square inside, polished and coated entirely with vermilion — built to hold a cremation urn. This matches the Shoku Nihongi record of Emperor Monmu's cremation (707), and together with the octagonal plan (reserved for sovereigns) underpins the theory that this is Monmu's true tomb.
Imperial Household Agency view
Not designated by the IHA; protected as a National Historic Site (1927, expanded 2024). The IHA attributes Emperor Monmu's mausoleum to the Hinokuma-Ako-no-Oka-no-e Ryo to the southwest (id:515), but archaeologists widely regard this mound as Monmu's true tomb.
Field notes
About 15 min on foot from Kintetsu Asuka Station; easily combined with Takamatsuzuka Kofun. The stone chamber was reburied after excavation and cannot be entered. A shoe-shaped stone object was found on the east side of the mound.