Dunboy Castle was the scene of the famous Siege of Dunboy in the summer of 1602 which ultimately led to its destruction and the breaking of the power of the O'Sullivan Bere. At that time Donal Cam O'Sullivan Bere was in rebellion against the English crown and Elizabeth I had sent a 5000-strong army under the command of Sir George Carew to suppress the insurgents. Even with its small garrison of 143 men Dunboy Castle was thought to be impregnable but following a fierce artillery bombardment the walls were smashed and after some desperate hand-to-hand fighting amid the rubble the defenders were finally overcome. The 58 survivors of the two-week siege were executed in the nearby market square.