Before the latter half of the fourth century, keyhole-shaped mounds were mainly seen in the Kinai, Seto Inland Sea (such as Kibi County) and northern Kyushu (such as Chikushi County) regions.
前方後円墳の分布は4世紀後葉前まで、主に畿内～瀬戸内海沿岸（吉備国など）～北九州（筑紫国など）に集中していた。