Satomi clan
Most of the Bōsō Peninsula was controlled by the powerful Satomi clan during the Sengoku period. The Satomi fought numerous battles with the Later Hōjō clan of Odawara for control of the Kantō region. In 1580, Satomi Yoriyoshi built Tateyama Castle in southern Awa Province to guard the southern portion of his territories and increase his control over the entrance to Edo Bay. The castle is rebuilt by his son, Satomi Yoshiyasu in 1588, who also built a fortified residence, or "jinya" at Katsuyama, and what is now part of the city of Kamogawa to protect the northeastern approaches to Tateyama Castle. Following the Battle of Odawara in 1590, the Kantō region was assigned to Tokugawa Ieyasu, who confirmed the Satomi as daimyō of Awa and Kazusa Provinces, with revenues of 92,000 "koku". Following the Battle of Sekigahara, Satomi Yoshiyasu also gained control of Kashima District in Hitachi Province, which increased his holdings to 122,000 "koku". After his death in 1603, his territories were inherited by his son, Satomi Tadayoshi. However, Satomi Tadayoshi was related by marriage to Ōkubo Tadachika, and was implicated in the Ōkubo Nagayasu Incident of 1614, which the Tokugawa shogunate used as excuse to abolish Tateyama Domain and extinguish the Satomi clan.