At the time of the Domesday Book Taunton belonged to the Bishop of Winchester, who had a minster or Augustinian Priory on the site. Between 1107 and 1129 William Giffard the Chancellor of King Henry I, converted the bishop's hall into a castle. In 1216, Bishop Peter des Roches, a supporter of King John, defended the castle during a barons' revolt. By the late 12th century the keep measured by with a first floor great hall over a stone vaulted undercroft. During the Second Barons' War it was used as a prison for the son of Simon de Montfort who was held here until 1282. In 1451, when the Earl of Devon besieged the castle which was held by Lord Bonville, it was arranged around two baileys.