From the beginning, there were many Kokujin-shu (local samurai) with independent spirits, and it is thought that the castle needed to have Kuruwa, which contain large residences, so as to help establish a coalition government with them.
もともとこの地域は自立意識の高い国人衆が多く、彼らと連合政権のような政治を実施していくために、城郭も広い屋敷をもつ曲輪が必要であったと思われている。