It is said that most castles built during the middle ages (mainly yamajiros [mountain castles]) contain many kuruwas of small area, while those built during the early modern period (mainly hirajiros [flatland castles]) often contain a lesser number of kuruwas of larger area.
中世の城郭では（主に山城）多数の小規模な曲輪をもつものが多く、近世の城郭（主に平城）では少数の大規模な曲輪をもつものが多いと言われる。