After the fall of the Hirai clan, Ryūzōji Takanobu moved his residence to Suko Castle.[4] Takanobu made extensive renovations to the castle, adding new kuruwa walls, earthworks, fortifications, a double moat, and a koguchi entrance, expanding it to 560 m on east-west axis and 580 m on north-south axis, making it the largest flatland-mountain castle in Saga Prefecture.[3] As a result of the renovations, it became an important castle that effectively ruled and controlled northern Kyushu.