Hachiouji Castle was a mountain castle built by Houjou Ujiteru on Mt. Fukazawa in 1587 in a strategic part of West Kantou (now Tokyo). Hachiouji, or "Eight Princes", was so named because the eight sons of the eight Buddhist Gozu Tenno deities were enshrined at the summit of the mountain.

Ujiteru made Hachiouji his main fortress, but in 1590 during the Siege of Odawara, Ujiteru and his main vassals raced to join the battle at Odawara, leaving only a few vassals, troops, mobilized peasants and their families—in all around 1000 to face the 15,000 of the combined armies of Toyotomi Hideyoshi, Uesugi Kagekatsu, Maeda Toshiie, and Sanada Masayuki.

The castle was overrun and fell in a single day. Yokochikenmotsu Yoshinobu, the chamberlain, and the other vassals committed seppuku because they had not been able to take decisive action. The women and children killed themselves or threw themselves into the waterfall of the lord's palace, starting with Ujiteru's wife Hisa. Stories say that the waterfall ran with blood for three days and three nights.

Tokugawa Ieyasu later abandoned the castle.

The castle ruins were declared a historical landmark on June 9, 1951.