The tyranny of King John caused great discontent amongst the barons, with whom Fitzwalter agreed in sentiment, and this discontent was brought to a head, driving the barons to take up arms, by a flagrant attempt on the honour of Fitzwalter's family. Matilde, "the fair," his daughter was exceedingly beautiful, and John attempted her chastity, which she indignantly repelled; "whereupon," says Stow, "and for other causes of the like sort, there ensued a war throughout the realm. The barons being received into London did great damage to the king; but in the end the king did not only banish the said Fitzwalter, among others, out of the realm, but also caused his castle and other houses to be demolished. After that a messenger was sent to Matilda the Fair about the king's suit, but she not consenting to it, was poisoned." This was done at Dunmow, by sprinkling a deadly poison on a poached egg, which she ate. Her exiled father retired to France, and entered into the service of the king. In the year 1214, John of England invaded France, and concluded a truce with the French for five years. The two armies lying on each side of a river one day, soon after the signing of the treaty, an English knight of great strength and valour came forth and challenged any French knight to a joust, when Fitzwalter crossed the river in acceptance thereof, and at the first course unhorsed his antagonist in gallant style. "By God's truth," exclaimed John, "he is a king indeed who is followed by such a knight as that!" "He is your own knight, O king," said one of his attendants, "Robert Fitzwalter whom you banished." Upon this the king sent for him to his tent, restored him to favour, gave him back his estates, and granted him permission to repair his castle and houses. The tyranny of the king, however, compelled the barons again to take up arms, to establish on a sure basis the laws and liberties granted by Edward the Confessor, of whom Fitzwalter became the head by the title of "Marshal of the Army of God and of the Church." Eventually they obtained the reluctant signature of the Magna Charta at Runnymede, when Fitzwalter was one of the twenty-five barons appointed to enforce the observance of the charter. In the reign of Henry III. he fought with great bravery under the baronial banner at the Battle of Lincoln, where he was taken prisoner, but was not detained long, as the next year he went as a crusader to the Holy Land, and displayed great valour at the siege of Damietta.