The Oxford Parliament (1258), also known as the Mad Parliament and the First English Parliament, assembled during the reign of Henry III of England. It was established by Simon de Montfort, 6th Earl of Leicester. The parlour or prolocutor (Speaker) was Peter de Montfort under the direction of Simon de Montfort. Simon de Montfort led the Parliament and the entire country of England for 18 months, from 1264 until his death at the Battle of Evesham.
King Henry III of England had agreed with Pope Innocent IV that his (Henry's) son Edmund should become King of Sicily following the death of Frederick II, Holy Roman Emperor. The Pope offered to partly fund the efforts to overthrow the Holy Roman Empire forces still in Sicily, but following Innocent's death and the succession of Pope Alexander IV, issues began to arise. Alexander did not want to fund the ongoing efforts, and should Henry not complete his task then he would be excommunicated. As a result, the King sought further taxation to repay his efforts from Parliament, existing Royal funds failing to cover debts owed, even after selling Edward's lands to William de Valence.
In the parliament in London on 2 April 1258, the great magnates' disaffection with the King reached a breaking point. An agreement was made to look at the issues of supply on behalf of the King, to which Henry and Edward agreed on 2 May. At the Oxford Parliament on 11 June, led by Simon de Montfort, Henry accepted a new form of government, laid out in the Provisions of Oxford, in which power was placed in the hands of a privy council, a council of fifteen members who were to supervise ministerial appointments, local administration and the custody of royal castles. Parliament, meanwhile, which was to meet three times a year, would monitor the performance of this council.
Henry agreed to these terms, and as a result a parliament consisting of fifteen was formed. These members included both Montfort, and Peter de Montfort, who acted as parlour or prolocutor for the proceedings. The remaining twelve consisted of Boniface of Savoy in his role as the Archbishop of Canterbury, Walter de Cantilupe as the Bishop of Worcester, the Earl of Norfolk, the Earl of Gloucester, the Earl of Hereford, the Earl of Warwick, the Earl of Albemarle, Hugh de Bigod, Peter de Saveye, Roger de Mortimer, James de Audeleye and John Maunsel.
The resolution of the Parliament did not last for long. The Pope excused the King of his obligations related to the throne of Sicily, meaning that he no longer required the funds provided by the additional taxation given to him by Parliament. The issue was one which was brought before King Louis IX of France, acting as arbitrator between Henry and the Barons at the Mise of Amiens. Louis made a decision entirely in favour of his fellow King, overturning the agreement made at the Oxford Parliament and absolved Henry's need to allow Parliament to appoint ministers, instead restoring that power to him.
This soon resulted in the Second Barons' War, with forces led by Simon de Montfort rebelling against the King. Following an initial attack by the Barons, Henry's feudal army was summoned and won a battle at Northampton. The forces of Montfort and Henry failed to come to terms, resulting in the Battle of Lewes where the Barons were victorious and the Mise of Lewes resulted. Prince Edward escaped his captors within a few months, and began to re-conquer England. The forces of Montfort found themselves trapped at Evesham, and in the ensuing battle, he was killed and his forces were routed by Edward's. The Barons continued to resist, but the Dictum of Kenilworth in October 1266 granted pardons, resulting in their surrender.
The parliament came to be known as "Mad" as a result of an entry in Liber de Antiquis Legibus which read "Hoc anno fuit illud insane parliamentum apud Oxoniam". However, historians Dr A.G. Little and Dr R.L. Poole have shown that the word "insane" was overwritten in the original text, and may have originally read "insigne" instead.