given custody of Horston Castle in Derbyshire, but by 1253 was back in Gascony. Montfort accompanied the King's son, the future Edward I, to Spain when he married Eleanor of Castile in the summer of 1254, and on 19 September of that year acted as surety at Bordeaux for the King's debts. For the next two years he was sent on diplomatic missions by Henry III; however his foreign service appears to have ended in 1257, by which time he was a member of the royal council, had received an appointment in the Welsh Marches, and was serving as High Sheriff of Staffordshire and Shropshire. In April 1258 he and Simon de Montfort were among the seven magnates who revolted against Henry III (the Second Barons' War). He and the Earl were also among the twelve magnates who drew up plans for reform (the Provisions of Oxford), and were on the council of fifteen members set up to govern England in the King's name. He presided over a Parliament at Oxford in 1258, dubbed the "Mad Parliament" by the King's supporters, and was thus the earliest recorded presiding officer of the Commons, an office later known as Speaker, but then referred to as 'parlour' or 'prolocutor'. In the autumn of 1259 he was with the King and Queen when they travelled to France to arrange a peace with Louis IX. In the same year he was named an executor of Simon de Montfort's will. On 12 April 1261, shortly before his death, Pope Alexander IV issued a papal bull which absolved Henry III of the oath he had taken to keep the Provisions of Oxford; when the King made this known in June of that year, Peter de Montfort was one of three arbitrators elected by the barons to negotiate with the King on their behalf. According to Cokayne, Montfort 'was now beginning to associate himself definitely with the baronial party', and as a result, the Sheriff of Warwickshire was ordered to prevent him from fortifying Beaudesert Castle. He took part with other barons in attacking Worcester, which fell on 28 February 1263 after several assaults. A temporary peace between the King and the barons was arranged in July of that year, and Montfort was given charge of Corfe Castle and Shirburn Castle. Simon de Montfort had left England after Henry III's return to power, but was back in the