Siege of Arai
- Hojo Soun vs. Miura Yoshiatsu
- Date: 1516
- Location: Sagawa
- KIA: Miura Yoshiatsu, Miura Yoshimoto
- Castle Siege
- Japanese: 新井城の戦い (arai jou no tatakai)
Miura Yoshiatsu and his son Miura Yoshimoto allied with the Ogigayatsu branch of the Uesugi clan and opposed the Hôjô's activities in Sagami province. Yoshiatsu's attempts to reduce the Hôjô's forward forts failed, however, and strife within the Uesugi allowed the Hôjô to turn their full attention on the Miura clan. In September 1512 Hôjô Sôun was in a position to lay siege to Yoshiatsu at Okazaki Castle, a critical part of the Miura's defense of the Miura Peninsula. Yoshiatsu was forced to quit Okazaki and retreat to Arai castle, a castle held by his son Yoshimoto. The Hôjô and Miura skirmished near Kamakura on a number of occasions as Sôun reduced the Miura's remaining outer forts, effectively bottling up Yoshiatsu at Arai. With the Miura reduced to only Arai, Sôun was content to let them 'wither on the vine' for almost three years. Finally, in 1516, Sôun ordered an all-out attack on the starving defenders of the castle and Yoshiatsu and Yoshimoto, after a brave stand, both committed suicide. Yoshimoto is famed for having cut off his own head, an act which, whether true or not, is said to have greatly impressed the Hôjô.