The height of the mound of the inner castle is about 8 meters (26 ft) along the Ohori Moat (Big Moat), 12 metres (39 ft) on the east side, 17 metres (56 ft) at the southeast corner of the "mizunote", and 16 metres (53 ft) to the west of the "hon-maru" above sea level. On the north side, although most of the mound is damaged, it can be inferred that it was about 10 metres above sea level if we consider the detailed accounts of "The Illustrated Map of All Fukuoka and Hakata". Except on the southern side, the mound of the inner castle was usually characterized by a "koshimaki-sekirui" or a "mizutataki-ishigaki" (a revetment constructed at the lower part of the mound), some of which can still be seen. In addition, around the gates were strengthened stone walls, which are 10 metres (33 ft) high.