Mortimer was one of the most powerful marcher barons of Henry III's reign and preoccupied with resisting Welsh advance. His mother was a daughter of Llywelyn ab Iorwerth. In 1258, Mortimer stood with the baronial opposition to Henry III. But de Montfort's rapprochement with Llywelyn ap Gruffydd, with whom Mortimer was constantly at feud, caused him to change sides. He fought with the losing royal army at Lewes in 1264 and subsequently helped Prince Edward to escape captivity. He took a leading part in de Montfort's defeat at Evesham in 1265.
Subjects: British History.