The time of the construction is unknown but it was used as the military base of Oyama clan during the Rebellion of Oyama Yoshimasa (1380-1382). The Oyama clan was an honorable family and its successive family heads were assigned as the governor of Shimotsuke province in the Kamakura period (1192-1333). At the time of the rebellion, Yoshimasa was in the conflict with Utsunomiya Mototsuna for the position of the governor and its territory. He defeated Mototsuna in the battle of Mobara, but he was forced to surrender when Ashikaga Ujimitsu, the Kamakura Kubo (the governor-general of Kamakura) raised a force of soldiers and attacked Washi Castle. Later, Yoshimasa rose in revolt again using branch castles of Chofuku, Shuku, and Iwatubo as the bases, to which Ashikaga Ujimitsu augmented his forces and made an attack on Oyama area. Yoshimasa finally surrendered and the history of Washi Castle ended in the battle. At the present time, the remains of the earthwork with a height of 2 m, the watch tower and the castle entrance are preserved. This is a valuable historic site as the ancient battle field.