A mountain castle ruin east of Ueda City, known as a key Sanada clan branch castle. The main bailey sits at approximately 790m elevation, utilizing steep terrain for defense. Famous as the 'impregnable' castle where Takeda Shingen suffered a major defeat in 1550 ('Toishi Kuzure'). During the First Battle of Ueda (1585), Sanada Nobuyuki launched his flanking attack from here against Tokugawa forces…

The founding date is unknown, but it functioned as a branch castle of Murakami Yoshikiyo. In 1550, Takeda Shingen attempted to capture it but suffered a major defeat due to steep terrain and solid defenses. This defeat, known as 'Toishi Kuzure,' is counted among Shingen's few losses. Later, Sanada Y…