He was the son of the French soldier Simon de Montfort. As leader of the baronial opposition to Henry III, he campaigned against royal encroachment on the privileges gained through Magna Carta, and defeated the king at Lewes, Sussex, in 1264. The following year he summoned a Parliament, which included not only barons, knights, and clergymen, but also two citizens from every borough in England. He was defeated and killed by reorganized royal forces under Henry’s son (later Edward I) at Evesham.