[1] In the late Nara period, after the establishment of a centralized government under the Ritsuryō system, the imperial court sent a number of military expeditions to what later was designated Mutsu Province in northern Japan to bring the local Emishi tribes under its control.

In 803 AD, Shiwa Castle, a large fortification with wooden walls, was established in what later became part of the city of Morioka to serve as an administrative center of the imperial government.

There was a gate at the center of each side facing each of the cardinal directions, with yagura watchtowers were erected at 60-meter (200 ft) intervals.

Within was a secondary palisade roughly 150 meters (490 ft) square, containing the 14 buildings making up the administrative compound.

[4] A large scale archaeological investigation was conducted by the Iwate Prefectural Board of Education from 1976 to 1977, in conjunction with the construction of the nearby Tōhoku Expressway.