 Custody of Rochester Castle remained with the Archbishops of Canterbury until the end of the 12th century . Despite ascending to the throne in 1199 King John did not confirm Hubert Walter as the castle 's custodian until July 1202 . John may have wished to regain direct control of what was an important castle . The crisis of John 's rule began in 1212 with the discovery of a plot to overthrow him . Defeat at the Battle of Bouvines in July 1214 marked the end of John 's ambitions to retake Normandy and exacerbated the situation in England . He returned to England in October and a few months later barons in the north of England were actively challenging his rule . A group of barons renounced their feudal ties to John in May 1215 , and they captured London , Lincoln , and Exeter . John persuaded Stephen Langton , the new Archbishop of Canterbury , to cede control of Rochester Castle to a royal constable , Reginald de Cornhill . Under the terms of the agreement , the castle was to revert to the control of the archbishop at Easter 1215 . This period was later extended to Easter 1216 . Letters Patent dated 25 May 1215 requested that other royal constables would take over from Cornhill . The castle would still be returned to the archbishop when the agreement expired or if peace was restored to the kingdom before Easter 1216 . In the meantime , control reverted to Langton whom John had asked to hold the castle " in such a way that by it no ill or harm shall come to us or our kingdom " . 
