Although the exact construction period of the Shimoyama-jo Castle is unknown since excavations have not been conducted, it is believed to have been built during the Warring States period. The lord of the castle is said to have been the Ban clan that ruled the area.
The castle, surrounded by embankments 5 meters in height, is approximately 50 meters on each of the 4 square sides. Most of the castles built in the Koka region are square in shape, and Shimoyama-jo Castle is a good example of the characteristics of castles in Koka.