As a mountain castle was changed into a flatland castle or a low mountain castle, a new main castle was constructed at the foot of a mountains and a former mountain castle was used as a Tsume-no-shiro (a castle that guards the back of the main castle) (such as Hagi Castle) or a castle site was moved to a low hill or flatland (such as Fukuyama Castle (Bingo Province)).
山城から平山城・平城に移行するにあたっては、麓に新たに主郭を築いて旧山城を詰の城（萩城など）とする例や、城地を低い丘や平地に移転する例（福山城(備後国)など）があった。