This is a flatland-mountain castle where Fujiwara no Tsunekiyo and his son, Kiyohira are said to have resided in the late Heian period (the 11th century). It is also called “Iwayadou Fortification” or “Shakushi Castle.” The main compound stood at the northern top of the hill (an altitude of 115 m) on the right bank of the Hitokabe River. On the southern hillside stood the second, third, and outer compounds. The eastern side of the castle area forms a steep slope facing the Hitokabe River. The koshiguruwa (the area bounded by earthworks) was arranged on the gentle decent of the western hillside. The compound that is supposed to have been Honmaru (the main compound) is in the precinct of the present Hachiman Shrine at the northern peak. The main compound was 90 m square in size, around which the remains of the earthworks can be seen. Beside the shrine stands a huge ginkgo tree that is said to be 800 years old. At the present the castle ruin is used as a playing field of Iwayadou High School. The area to the southwest, where the school building of Iwayadou High School and Iwayadou Elementary School are located is supposed to have been the site of the outer compound.