Koriyama Castle was the stronghold of Mori Motonari. Using it as his base, he contended with the two great powers of the Ouchi and Amako clans to establish supremacy over the Chugoku region. In the 1540–41 Siege of Yoshida Koriyama Castle, he withstood a massive Amako army with a small force and repelled them together with Ouchi Yoshitaka's relief troops — a victory that launched the rise of the Mori clan.