A scholar of military science in the Edo period classified castles based on topography into three types: 'Hirajiro' (a castle built on flatland), 'hirayamajiro' (castles built on a hill or low mountain surrounded by a plain) and 'mountain castles.'
江戸時代の軍学者による地勢に基づく城の分類には、「平城（ひらじろ）」・「平山城（ひらやまじろ）」・「山城（やまじろ）」・の3つがある。