Abstract
The Akita Fortress was built in 733 and maintained throughout the 8th century as an isolated fortress beyond the limit of Yamato Dynasty's real control. The dynasty did so because it thought necessary to have an outpost there to properly receive (and occasionally refuse) diplomatic delegations from Balhae/Bohai. Because of the irregularity and unpredictability with which those delegations arrived, the dynasty once decided to abolish the Akita Fortress in 770 but withdrew the decision ten years later. The very existence of the Akita Fortress depended on Balhae/Bohai delegations until the end of the 8th century when the Balhae/Bohai delegations changed the navigation route to Japan: as they learrned by then to build ships large enough to cross the Sea of Japan directly to the Noto Peninsula, they abandoned the northern route via the western coast of Hokkaido. The Akita Fortress then lost its diplomatic functions, which affected even its physical appearance.
