From descriptions in the "Nihonshoki" (Chronicles of Japan), it has become clear that at least one ruler, King Osasagi (Emperor Nintoku), made his base in Osaka and developed the Kawachi Plain; evidence of river improvement (the Naniwa-horie canal) and embankments (Manda-no-tsutsumi levee) can still be seen today.
日本書紀の記述などから少なくともオオササギ王（仁徳天皇）は大阪に本拠を置き河内平野を開発したことが判っており、当時の河川改修痕跡（難波の堀江）や堤防痕跡（茨田堤）も残存している。