Kogo-ishi or kogo-ishi style mountain castles were castles built on mountains in ancient times, and because there is no description of them in the 'Nihon shoki' (Chronicles of Japan) or 'Zoku Nihon shoki' (the sequel to Chronicles of Japan) they can be identified only through remains.
神籠石（こうごいし）または神籠石式山城（こうごいししきやましろ）とは古代に築造された山城で、「日本書紀」「続日本紀」に記載がなく、遺構でしか存在の確認できないものを指す。