Lambeth, treaty of (11 September 1217) William Marshal, Earl of Pembroke, acting as regent for the nine year old Henry III was the main force and impetus for the defeat of Philip II of France. In May 1217, at the age of 70 Marshal lead the attack to defeat the French at Lincoln. Following this defeat, and one at Sandwich, Marshal negotiated a Treaty, signed at Lambeth Palace, which ended the war. Marshal went on to win round the English barons, who had supported Philip II against King John, securing peace and order in England.