Book of Song
Yamato rule is usually believed to have begun about 250 AD, and it is generally agreed that Yamato rulers had keyhole-kofun culture and hegemony in Yamato until the 4th century. Autonomy of local powers remained throughout the period, particularly in Kibi (the present-day Okayama Prefecture), Izumo (current Shimane Prefecture), Koshi (current Fukui and Niigata Prefecture), Kenu (northern Kantō), Chikushi (northern Kyūshū), and Hi (central Kyūshū). During the 6th century, the Yamato clans began to dominate the southern half of Japan. According to the "Book of Song", Yamato relationships with China probably began in the late 4th century.