Taika Reform
The Bōsō Hill Range was settled from the earliest periods of Japanese history. The Yōrō Ravine in present-day Ōtaki, Chiba is home to Jōmon period remains. Kofun tumuli were built across the entire hill range in the Kofun period, but Futtsu and Ichihara have especially rich examples of tumuli. Under the Taika Reform of 645, during the Asuka period, the hill range became part of three provinces, Shimōsa Province to the north, Kazusa Province in the middle part of the range, and Awa Province to the south. The hill range is noted for its richness of castles built during the Sengoku period as part of medieval conflicts.