Miyakonojo was an impregnable fort, having Miyakonojo as a main castle, which was protected by 12 outer castles: Tsuneyoshi-jo Castle, Umekita-jo Castle, Shiwachi-jo Castle, Kajiyama-jo Castle, Katsuoka-jo Castle, Yamanokuchi-jo Castle, Gassan Hyuga-jo Castle, Yasunaga-jo Castle, Nonomidani-jo Castle, Sueyoshi-jo Castle, Yamada-jo Castle, and Takarabe-jo Castle.
都城は、都之城を本城とし、恒吉城、梅北城、志和池城、梶山城、勝岡城、山之口城、月山日向城、安永城、野々美谷城、末吉城、山田城及び財部城の12箇所の外城に守られており、容易に攻めることはできない。