In the Barons' War of 1215–17 the castle was attacked again, prompting further improvements in its defences. In 1220 Falkes de Breauté, who controlled many royal castles in the middle of England, demolished the Church of St Budoc to the south-east of the castle and built a moated barbican to further defend the main gate. The remaining wooden buildings were replaced in stone, including the new Round Tower which was built in 1235. King Henry III turned part of the castle into a prison, specifically for holding troublesome University clerks, and also improved the castle chapel, replacing the older barred windows with stained glass in 1243 and 1246. Due to the presence of Beaumont Palace to the north of Oxford, however, the castle never became a royal residence.