Ōnojō Fortress Ruins

Onojo Fortress was built in 665 on Mt. Shioji, just north of Dazaifu, making it the oldest known mountain fortress in Japan. Its construction was ordered after Japan and its ally Baekje suffered a major defeat against Tang China and the Korean kingdom of Silla in 663. Eight kilometers of earthen and stone walls enclosed a summit command post overlooking Hakata Bay. Exiled Baekje nobles provided the construction expertise, patterning the fortress after mountaintop defenses from their homeland. Excavators have uncovered 9 gates and around 70 buildings. The fortress remained manned until roughly the tenth century.