A collective term for the burial mounds scattered on the hills facing the Genkai. Over a wide range of about 8km north-south and about 2km east-west, the Katsuura Kogen mound, Katsuura Minohata mound, Niihara/Nuyama mound, Sudata mound, Miyachi Takekoko mound, Temitsu Wagiri mound, etc. It consists of a total of 60 groups of one mass. It is designated as a national historic site except for some. The tumuli were built in the 5th to 7th centuries. The tomb group of the Munakata clan, an ancient royal family who nurtured their faith in Okinoshima. Among them, the Niihara-Nuyama Kofun group is registered as a constituent asset of the World Heritage Site "" Kamijuku Ruru Island "Munakata, Okinoshima and Related Heritage Group".