Constructed in 1335, Kosuiji Castle had been resided by successive family heads of Shiba clan, which was one of the powerful branch families of Ashikaga clan. The castle stood at the top of the terraced hill with an altitude of 180 m on the right bank of the Kitakami River. The castle area was 550 m east to west and 700 m north to south, where Kichibei-Yakata (Kichibei’s Residence) stood in the southwest, to the west of which stood Nishi-gosho (the west residence). The size of Honmaru (the main compound) was 60 m east to west and 120 m north to south, and that of Ninomaru (the second compound) was 50 m east to west and 100 m north to south. The terraced koshiguruwa (the area bounded by earthworks) was built adjacent to each compound. Details about dry moats and earthworks are unknown; however the remains of the double- or triple-structured moats can be seen from the middle of the hillside down to the bottom of the hill in ever direction except the eastern hillside, which drops off precipitously. In 1928 the Showa Emperor dropped in at this castle ruin to have nodate (the tea ceremony outside) during a military exercise, in memory of which a cherry tree was later planted. Since then a lot more cherry trees were planted and the castle ruin is now known as one of the major cherry blossom viewing spots.