|The Reign of William the Conqueror|
The Duke and his neighbours
The glory of the triumph (1067) and the booty of his conquest did not enable William to obtain peace at the frontiers of the Duchy. On the contrary, his power disturbed his neighbours who took every opportunity to challenge it.
William lost the alliance of Flanders. The succession to Baldwin V, father of Matilda, was to the advantage of Robert le Frison, an enemy of the Duke of Normandy, following the disaster of the Norman Cassel expedition (1071). The Duke thus also risked losing Maine, the protective buffer against his enemies of Anjou and Blois. The Count of Anjou came to the aid of the burghers of Le Mans who were hostile to the Normans. A significant expedition, involving an alliance of English mercenaries, was required in 1073 for its re-conquest. The longest stay of the Duke-King in Normandy, between 1076 and 1080 was occupied by similar interventions in Maine and Brittany. He had to return in 1084 to lay siege to his castle of Sainte-Suzanne, as Hubert, Viscount of Le Mans had rebelled.
William's enemies were supported by the King of France, Philip I. He had the most to fear from the rise in power of the Duke of Normandy of whom he was theoretically overlord. Thus when Robert Curthose revolted against his father in 1077, King Philip I welcomed him and gave him the fortress of Gerberoy at the frontiers of Duchy. William laid siege to his own son from 1078-1079 before the King of France arranged a reconciliation.
All these difficulties were played out on the borders. Within the Duchy the authority of William was complete. This was further demonstrated at the Council of Lillebonne in 1080. Favourable to the reform of the conduct and discipline of the clergy he refused to surrender to the Pope his control over the ecclesiastical hierarchy.