Morioka-jō, first named Kozukata-jō, was begun in 1592 by daimyō Nambu Nobunao as a strategic fortress overlooking the confluence of the Kitakami and Nakatsu Rivers - important trade routes in Northern Honshū. Nobunao's son Shigenao completed the castle in 1633, and it remained the center of the Nambu family's rule until the Meiji Restoration. Out of respect for the Tokugawa Shogunate, a central keep (donjon) was never built. The name of the castle was officially changed to Morioka-jō sometime in the 17th century. All of the castle structures were completely dismantled in 1871, after which the site became the park of Iwate-kōen. Only the sturdy stone walls of the castle remain today.