Yoritomo’s Uprising, Defeat at Ishibashiyama and Entry into Kamakura

Yoritomo began his uprising in Izu in the eighth month of 1180 after receiving Prince Mochihito’s call against the Taira. Hōjō Tokimasa and other local allies helped organize the attack on Yamaki Kanetaka, a Taira-aligned figure exercising power in Izu. The Sasaki brothers and other followers assaulted the residence, killed Kanetaka and burned the buildings. The later Azuma Kagami describes preparations and routes in detail, from the viewpoint of the government Yoritomo eventually founded.

The first success was followed by defeat at Ishibashiyama in Sagami on the twenty-third day of the eighth month. Ōba Kagechika’s forces attacked before Yoritomo could unite with all his expected allies. Heavy rain and difficult river crossings hindered movement. Yoritomo escaped into the mountains with assistance from followers including Doi Sanehira, then crossed by sea to Awa on the Bōsō Peninsula.

Eastern warriors, including the Chiba and Kazusa groups, joined him there. With a larger coalition, he returned toward Sagami and entered Kamakura on the sixth day of the tenth month. Construction of his residence at Ōkura followed, and a Samurai-dokoro organized warrior service under Wada Yoshimori. These arrangements supplied a headquarters and channels for commanding followers.

Kamakura already had settlements and transport connections; archaeology has recovered evidence of an earlier administrative center. Yoritomo’s entry therefore reorganized an inhabited place. The defeat in Sagami had shown the limits of his initial following, while the Bōsō regrouping and Kamakura headquarters made sustained mobilization possible. Victory over the Taira and wider court recognition still lay ahead.