Sannohe Castle

Sannohe Castle was a hilltop castle (hirayamajiro) in Sannohe Town, Sannohe District, Aomori Prefecture, also known as Tomegasaki Castle. It is said to have been built in 1539 by Nanbu Harumasa after his previous residence, Seijuji Hall, was burned down by a retainer's arson. Sannohe Castle served as the Nanbu clan's principal castle until Nanbu Nobunao relocated the clan's base to Morioka Castle. The castle site was designated a National Historic Site on March 15, 2022.

Location and Structure

The castle stands on a river terrace formed by the erosion of the Mabe and Kumahara rivers, both of which served as natural moats, making it a naturally defensible stronghold. The castle grounds extend about 1.5 km east-west and about 400 m north-south, with a height difference of roughly 90 m from the surrounding lowlands.

Lords and Succession

After its construction in 1539, Sannohe Castle served as the principal castle of successive Nanbu clan lords throughout the Sengoku period, also functioning as a base for controlling the clan's rapidly expanding retainer band. Its role ended when Nanbu Nobunao relocated the clan's base to Morioka Castle.

Current State and Preservation

The castle ruins were designated a National Historic Site as "Sannohe Castle Ruins" on March 15, 2022, and are maintained and open to the public as "Historic Site Sannohe Castle Ruins Shiroyama Park." Stone walls, moat remnants, earthworks, and masugata gate structures from that era can still be observed today.