[1] In the Nara period, after the establishment of a centralized government under the Ritsuryō system, the imperial 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.

Per the Shoku Nihongi, following a huge earthquake in the year 715 AD, a large number of people migrated to this area from the southern Kantō region, forming numerous fortified settlements in the hinterland.

An inscription on a monument found at the site of Taga Castle gives a foundation date of 724 AD and states that it was constructed by Azumabito Ono as the provisional provincial capital of Mutsu Province.

Along with Akita Castle and Okachi Fort in Dewa Province, it was one of the main bases for the Yamato re-expansion into northern Honshu.

Taga Caste gradually fell into ruins, and rise of Hiraizumi under the Northern Fujiwara in the twelfth century saw its final demise.

The fortification was a square enclosure, approximately 3.4 kilometers in perimeter, consisting of a 5-meter high earthen rampart surmounted by a wooden palisade, and protected by a 3-4 meter wide dry moat.

[8] Matsuo Bashō (松尾 芭蕉) creatively recounts his viewing of the monument in Oku no Hosomichi (奥の細道), concluding 'there are seldom any certain vestiges of what has been, yet in this place there are wholly trustworthy memorials of events a millennium ago' and is moved to tears.