However, walls were not constructed around the capital cities in Japan because invasion by other races was not considered a threat because Japan was an island (Dazaifu might have been built with walls), although a castle with outer bailey (a capital surrounded by walls) was seen in the continent where invasion by different races was feared.
ただし、異民族の侵攻の恐れのある大陸においては、郭城（塀＝羅城をめぐらした城）であるが、島国である日本では城壁は作られず（大宰府には城壁があったとも考えられている)。