| Location | Osaka Pref. |
|---|---|
| Shape | Keyhole-shaped mound |
| Mound length | 335 m |
| Period | Late 6th c. |
With a total length of 335m, this is the fifth-largest burial mound in Japan. The rear circle is ~200m in diameter and ~23m high; the front section is ~220m wide and ~19m high. Located outside the main Mozu and Furuichi clusters, this late-6th-century mound rivals in scale the colossal 5th-century mounds, and is academically significant as a "terminal-phase giant kofun." It straddles the border of Matsubara and Habikino cities. As an IHA-designated imperial reference site, it has never been excavated. Sometimes called the "phantom giant kofun."Despite being the 5th largest in Japan (335m), it is little known—sometimes called the "phantom giant kofun"—partly due to its IHA reference-site status. Straddling Matsubara and Habikino cities, it stands as a third monumental mound between the Mozu and Furuichi groups. The late-6th-century date coincides with the eve of the ritsuryō state formation, raising the academic puzzle of why such a colossal mound was built at that stage. Whoever is buried here clearly ranked among the supreme power-holders of the age; some scholars suggest a Soga clan chieftain. IHA management restricts access to the exterior perimeter only. Even after the Mozu–Furuichi World Heritage inscription, this mound remains outside the designated zone, creating a striking gap between its actual size and its public recognition—making it a "giant kofun known only to the initiated" among kofun enthusiasts.
IHA-designated reference site (Otsuka Ryobo Sankochi); excavation prohibited. From exterior observation, part of the outer moat survives on the southern side. The mound profile reveals a distinctive "kenbishi-gata" (sword-lozenge) form where the rear circle rises significantly higher than the front section — a hallmark of late-Kofun monumental construction. The presence of stone paving and haniwa is unconfirmed; internal structure and grave goods unknown. Estimated dimensions from survey: rear circle ~200m diameter, ~23m high; front section ~220m wide, ~19m high; three-tiered. Despite being the 5th-largest mound in Japan (335m), it remains unexcavated — earning it the nickname "phantom giant kofun."