The appearance of the large keyhole-shaped tomb mounds from the mid third century, indicates the establishment of a unified authority and the family of the Great King at that time are thought to be the ancestors of the Imperial Family.
3世紀中期に見られる前方後円墳の登場は統一政権の成立を示唆しており、このときに成立した大王家が天皇家の祖先だと考えられている。