During the Second Barons' War, Simon de Montfort's victory at the Battle of Lewes in 1264 led to him becoming de facto ruler of England. He tried to set up a reformed government, including the first parliament elected by citizens of the towns, but was unable to retain the support of the other barons. Several switched sides to the royalist cause; Montfort was defeated at the Battle of Evesham on 4 August 1265, where he was killed along with his son. Eleanor fled to exile in France where she became a nun at Montargis Abbey, a nunnery founded by her deceased husband's sister Amicia, who remained there as abbess. There she died on 13 April 1275, and was buried there. She was well treated by Henry, retained her incomes, and her proctors were allowed to pursue her litigation concerning the Leicester inheritance in the English courts; her will and testament were executed without hindrance.