[1] In the late Nara period, after the establishment of a centralized government under the Ritsuryō system, the Yamato court sent a number of military expeditions to what is now the Tōhoku region of northern Japan to bring the local Emishi tribes under its control.

Tokutan Castle appeared to have been partially built on top of an earlier site, with dimensions of approximately 150 meters to a side, which was at an angle to, and extended further to the east than the later, larger, enclosure.

After its imperial garrison was withdrawn, the fortifications continued to be manned until sometime in the mid-9th century by the local Fushū (俘囚) militia (Emishi who were loyal to the Yamato court), but was eventually abandoned at some unknown time.

Despite its legally protected status, a large portion of the site was severely damaged by construction work during the reconstruction of Tokuda Elementary School.

The site is a park, containing the Yahaba Town History and Folklore Museum (矢巾町歴史民俗資料館) which displays a number of item recovered during archaeological investigations and construction work.