Some mountain castles stopped using their traditional wooden fences and started to use the architectural styles of flatland castles and low mountain castles, surrounded by mud walls with portholes, and became an impregnable fortification as if it were a pillbox (such as Takatori Castle).
また従来の木柵ではなく、平山城や平城の建築様式を取り入れ、狭間を持つ土塀で囲まれた、さながらトーチカのような鉄壁の要塞と化した山城もある（鷹取城など）。