Unlike in Continental Asai, walled towns did not develop in Japan with only a few exceptions partly because different races seldom invaded Japan and partly because most of the land is covered with mountains; 'Josaku' (official defense sites) constructed as military defense facilities and 'Yakata', or worriers' residences armed with moats and wooden framed stages, developed into mountain castles during the Middle Ages.
日本では異民族の侵入が少なかったことや山地が国土の大半を占めることなどから、大陸に見られるような城壁都市は一部を除いて発展せず、野戦用の防御施設として作られた「城柵」や武士の居館を堀や櫓で防備した「館（やかた、たて、たち）」が、中世には山城へと発展した。