Count of Amiens, to a monastery. Before he became a monk, Simon handed his county of the Vexin over to King Philip. The Vexin was a buffer state between Normandy and the lands of the French king, and Simon had been a supporter of William. William was able to make peace with Philip in 1077 and secured a truce with Count Fulk in late 1077 or early 1078. In late 1077 or early 1078 trouble began between William and his eldest son, Robert. Although Orderic Vitalis describes it as starting with a quarrel between Robert and his two younger brothers, William and Henry, including a story that the quarrel was started when William and Henry threw water at Robert, it is much more likely that Robert was feeling powerless. Orderic relates that he had previously demanded control of Maine and Normandy and had been rebuffed. The trouble in 1077 or 1078 resulted in Robert leaving Normandy accompanied by a band of young men, many of them the sons of William's supporters. Included among them were Robert of Belleme, William de Breteuil, and Roger, the son of Richard fitzGilbert. This band of young men went to the castle at Remalard, where they proceeded to raid into Normandy. The raiders were supported by many of William's continental enemies. William immediately attacked the rebels and drove them from Remalard, but King Philip gave them the castle at Gerberoi, where they were joined by new supporters. William then laid siege to Gerberoi in January 1079. After three weeks, the besieged forces sallied from the castle and managed to take the besiegers by surprise. William was unhorsed by Robert and was only saved from death by an Englishman, Toki son of Wigod, who was himself killed. William's forces were forced to lift the siege, and the king returned to Rouen. By 12 April 1080, William and Robert had reached an accommodation, with William once more affirming that Robert would receive Normandy when he died. Word of William's defeat at Gerberoi stirred up difficulties in northern England. In August and September 1079 King Malcolm of Scots raided south of the River Tweed, devastating the land between the River Tees and the Tweed in a raid that lasted almost a month. The lack of Norman response appears to have caused the Northumbrians to grow restive, and in the spring of 1080 they rebelled against the rule of