In the latter half of the third century and onward; large keyhole-shaped mounds which were considered to be imperial mounds, were significantly scaled up from the mounds in the early 'Kofun period' and appeared in Nara Basin.
3世紀の後半から奈良盆地に王墓と見られる前代より格段に規模を増した前方後円墳が出現した。