During the period of the Northern and Southern Courts, many battles (Tomo kassen) were fought between the Northern Court and the Southern Court in an area covering the sea off Tomonoura and the town of Tomo, thereby destroying invaluable cultural properties such as a five-storey pagoda of Seikan-ji Temple.
南北朝時代には鞆の浦沖から鞆にかけての地域で北朝と南朝との合戦（鞆合戦）が幾度もあり、静観寺五重塔などの貴重な文化財が失われた。