Tagajo was established in 724 by Ono no Azumahito as the provincial government seat and garrison headquarters of Mutsu Province, serving as the core base of the ritsuryo state's administration of Tohoku. The Nara- and Heian-period government office ruins are designated a Special Historic Site, and the Tagajo Monument is celebrated as one of the "Three Ancient Steles of Japan." The fortress also se…

Founded in 724 by Inspector Ono no Azumabito in Mutsu Province. It housed the Mutsu provincial government and garrison, serving as the frontline for Emishi relations. Burned during the Korehari no Azamaro rebellion in 780 but rebuilt. Designated a Special National Historic Site in 1966.