A giant keyhole mound spanning Matsubara and Habikino. It is 335m long; the front section is 230m wide and 4m high, and the rear circle is 185m across and 20m high. A moat surrounds it. Regarded as the last giant keyhole mound built in the Furuichi group, it is administered by the Imperial Household Agency as the Otsuka imperial mausoleum reference site.
Finds & research
A large boulder known as Gobo-ishi, thought to be a ceiling stone from a horizontal stone chamber, remains on the rear circle. Documents also indicate that part of a horizontal stone chamber was open until the late 18th century, but the complete burial facility and grave goods are unknown.
Official status & archaeological view
Official status
The site became the Otsuka imperial mausoleum reference site on September 21, 1925, and is administered by the Imperial Household Agency. An official government reply lists the occupant as unknown; it is not designated as the tomb of any particular emperor. The mound spans Matsubara and Habikino, is not freely accessible, and has not undergone an academic excavation.
Attribution (jitei): the Imperial Household Agency's determination of whose tomb it manages — separate from heritage designation.
Archaeological view
Matsubara City dates it to the mid-6th century or later, citing late-period traits: unclear evidence for haniwa, a low and widely flaring front section, and indistinct tiers on the rear circle (another city description gives about the late 6th century). The Imperial Household Agency’s fiscal 1986 survey of the outer bank, however, collected a haniwa fragment, probably from the neck of a morning-glory-shaped haniwa, at the foot of the mound. The occupant is unidentified.
Field notes
The mound is managed by the IHA and cannot be entered. Matsubara City suggests two ways to view it: from a Kintetsu Minami-Osaka Line train and from a prefectural-road overpass. From a train running from Kawachi-Matsubara toward Eganosho, the wooded mound can be seen to the south, and the overpass where the prefectural road crosses the tracks offers a view of the whole mound.