In 1256 Roger went to war with Llywelyn ap Gruffydd when the latter invaded his lordship of Gwrtheyrnion or Rhayader. This war would continue intermittently until the death of both Roger and Llywelyn in 1282. They were both grandsons of Llywelyn ab Iorwerth. Mortimer fought for the King against the rebel Simon de Montfort, 6th Earl of Leicester, and almost lost his life in 1264 at the Battle of Lewes fighting Montfort's men. In 1265 Mortimer's wife, Maud de Braose helped rescue Prince Edward; and Mortimer and the Prince made an alliance against de Montfort. In August 1265, de Montfort's army was surrounded by the River Avon on three sides, and Prince Edward's army on the fourth. Mortimer had sent his men to block the only possible escape route, at the Bengeworth bridge. The Battle of Evesham began in earnest. A storm roared above the battle field. Montfort's Welsh soldiers broke and ran for the bridge, where they were slaughtered by Mortimer's men. Mortimer himself killed Hugh Despencer and Simon de Montfort in crushing Montfort's army. Mortimer was awarded Montfort's severed head and other parts of his anatomy, which he sent home to Wigmore Castle as a gift for his wife, Lady Mortimer.