Kodai Sanjo refers to castles which was built in several locations of western Japan in ancient times and be written some statements in the 'Nihon-shoki' (the oldest chronicles of Japan) or 'Shoku Nihongi' (Chronicle of Japan Continued), or other lineage of these mountain castles.
古代山城とは、西日本各地に古代に造られた山城の中で、「日本書紀」「続日本紀」になんらかの記載がある諸城およびその系統の山城。