Takayasu Castle, Mountain fortress on Mount Takayasu, Japan

Takayasu Castle is an ancient mountain castle said to have stood on the summit of Mount Takayasu, a 487-metre peak at the southern end of the Ikoma range on the Nara-Osaka border. No clear walls, gates or other remains of the castle have been found; in 1978 a group searching for the site located the stone foundations of six buildings in the mountains, two of which were dated by excavation to the early 8th century.

The fortification was founded in 667 during a period of regional conflicts and served as a key point for controlling boundaries between two provinces. The site was abandoned in 701 and marked the end of its role as an active military installation.

The name appears in the Nihon Shoki, which records that in 667, alongside Kōgoishi-style mountain forts, Takayasu was built to defend the capital region after the defeat at Baekgang. In 669 Emperor Tenji climbed the ridge to inspect repairs but halted the work out of concern for the people's fatigue. In 672, during the Jinshin War, the Ōmi court's garrison burned its tax storehouses and fled.

No clear walls or remains of the fortress have been confirmed, so visitors should not expect marked ruins; the summit area is reached on foot and the western slope facing the Osaka plain is steep. Excavations by Osaka and Nara prefectures in the presumed area have found no definite structures. The summit also holds a weather radar station of the Osaka District Meteorological Observatory.

No clear walls or remains of Takayasu Castle have ever been found; its very outline is uncertain. In 1978 the group "Takayasu o saguru kai" found stone foundations in the mountains, drawing attention, but excavations dated two of the six buildings to the early 8th century, and later digs by Osaka and Nara found no definite traces.