A fortified Buddhist temple established in 1496 which was home to warrior monks, priests, peasants, and local nobles (Ikkou-ikki) who opposed samurai rule. Oda Nobunaga, who feared the power and influence of the monks, set siege to the fortress in 1570 while Kennyo was its chief abbot. The siege lasted for 10 years, and the temple finally fell in 1580.

Toyotomi Hideyoshi began construction of Osaka Castle on the same site three years later.