Like Odawara Castle, as a result of the repeated expansion of a castle that was originally a mountain castle and castle town at the foot of the mountain, both merged and developed into a large flatland castle surrounding its entire castle town by the sogamae (outer citadel).
小田原城のように、元々は山城であったものが、城と麓の城下町が拡張を繰り返した結果両者が一体化し、城下町全体を惣構えで囲んだ大規模な平山城に発展した例もある。