Ōshū Kaidō
The confluence of the Kitakami River and the Nakatsu River was of strategic importance in control of river traffic in central Ōshū. The location of the castle was also intended to control traffic on the Ōshū Kaidō highway from the capital to the northern end of Honshū island, and beyond to Ezo (modern Hokkaidō), and also traffic on a route across the Ōu Mountains which connected the Pacific and Sea of Japan coasts of Japan.