Moshiriya Chasi located in Shiroyama Kushiro City, Hokkaido was a fort built by the Ainu people. “Moshiriya” means “a fort on the river with an island” in the Ainu. It is said to have been built in 1751 by an Ainu named Tomikara Ayano. The ruin is the elliptical hill with a major axis of 170 m and a minor axis of 70 m. The fort had three terraces on the northeastern side and two on the southwestern side. The fort area was divided into the two compounds; the inner compound and the outer one. The inner compound was surrounded by a dry moat and earth from the moat was piled up along the moat to form the earthwork. The fort was also used for a festival and meeting place. At the present time, the ruin is surrounded with a fence and preserved as a National Historic Site (designated in 1935). This is a precious cultural property left by the Ainu people.