The Mise[a] of Lewes was a settlement made on 14 May 1264 between King Henry III of England and his rebellious barons, led by Simon de Montfort.

The conflict between king and magnates was caused by dissatisfaction with the influence of foreigners at court and Henry's high level and new methods of taxation.

In 1258, Henry had been forced to accept the Provisions of Oxford, which essentially left the royal government in the hands of a council of magnates, but this document went through a long series of revocations and reinstatements.

In 1263, as the country was on the brink of civil war, the two parties had agreed to submit the matter to arbitration by the French king Louis IX.

The conflict was caused by several factors: the influence of foreigners at court, a wasteful war over the crown of Sicily, and a personal dispute between King Henry and Simon de Montfort, Earl of Leicester.

In 1258, Henry was forced to accept the so-called Provisions of Oxford, whereby he effectively surrendered control of royal government to a council of magnates.

[6] Cornered, de Montfort had to accept a truce and agree to submit the issue to arbitration by the French king Louis IX.

[8] Hostilities started already in February, when de Montfort's sons, Henry and Simon the Younger, attacked the possessions of Roger Mortimer in the Marches.

[9] Henry summoned the feudal army, and the royal forces won an important victory at Northampton, where the younger Simon was captured.

Rather it was external circumstances outside of de Montfort's control that led to the eventual failure of the negotiations between the royalists and the barons.

Once the battle was over and government in de Montfort's hands, he had no longer any interest in reaching a compromise with the royalists, and that was why hostilities continued.

[22] The government led by de Montfort soon ran into problems; he faced poor finances, general disorder, and the threat of invasion from exiled royalists in France.

[23] It was decided – since the French arbitration committee had come to nothing – to set up a provisional administration, consisting of de Montfort, the young Earl of Gloucester, and the Bishop of Chichester.

[25] To keep the borders safe, Montfort had been forced to release Roger Mortimer and other royalist Marcher lords after the Battle of Lewes.

On 4 August 1265 de Montfort found himself trapped at Evesham, forced to give battle with a much smaller army than the royals.

In October 1266 the Dictum of Kenilworth set down terms by which the rebels could obtain pardons, and by the end of the year the garrison surrendered.