Robert Fitzwalter (died 9 December 1235) was one of the leaders of the baronial opposition against King John, and one of the twenty-five sureties of Magna Carta. He was feudal baron of Little Dunmow, Essex and constable of Baynard's Castle, in London, to which was annexed the hereditary office of castellan and chief knight banneret of the City of London. Part of the official aristocracy created by Henry I and Henry II, he served John in the wars in Normandy, in which he was taken prisoner by King Philip II of France and forced to pay a heavy ransom. Fitzwalter was implicated in the baronial conspiracy of 1212. According to his own statement the king had attempted to seduce his eldest daughter, but Robert's account of his grievances varied from time to time. The truth seems to be that he was irritated by the suspicion with which John regarded the new baronage. Fitzwalter escaped a trial by fleeing to France. He was outlawed, but returned under a special amnesty after John's reconciliation with the pope. Fitzwalter continued, however, to take the lead in the baronial agitation against the king, and upon the outbreak of hostilities in 1215 was elected "Marshal of the Army of God and Holy Church". It was due to his influence in London that his party obtained the support of the city and used it as their base of operations. The clause in Magna Carta prohibiting sentences of exile, except as the result of a lawful trial, refers more particularly to his case. He was one of the twenty-five barons appointed to enforce the promises of Magna Carta, and his aggressive attitude was one of the causes which contributed to the revival of civil war later in 1215. He was one of the envoys who invited Prince Louis to England, and was the first of the barons to do homage when Louis entered London. Slighted by the French as a traitor to his natural lord, he served Louis with fidelity until he was captured at the Battle of Lincoln in May 1217. Released on the conclusion of peace, he joined the Fifth Crusade, but returned at an early date to make his peace with the regency. The remainder of his life was uneventful, and he died peacefully in 1235. He was the father of three children: Matilda, Robert, and Christina (who married William FitzGeoffrey de Mandeville, 3rd