In 1051 William visited England. Two years later he married Matilda, daughter of Baldwin, Earl of Flanders, and a descendant of Alfred. The marriage had been forbidden by a council at Rheims as uncanonical, and was opposed by Lanfranc, Prior of Bec. This produced a quarrel between Lanfranc and William, who ravaged the lands of the abbey and ordered the banishment of its prior. Lanfranc, however, soon came to terms with the duke, and engaged to obtain a dispensation from Rome, which, however, was not granted till 1059. Strengthened by this alliance with Flanders, William showed himself more than a match for all his enemies. Henry, who had hitherto been for the most part friendly, now turned against him. After the suppression of some isolated revolts, William was threatened in 1054 by a great confederacy. His dominions were invaded by the forces of the French king, in combination with those of Geoffrey of Anjou, Theobald of Blois, and others. William remained at first on the defensive; then, falling suddenly on one of the French armies at Mortemer, in the north-eastern corner of his duchy, he cut it to pieces. This blow put an end to the war; Henry made peace (1055), and William took the opportunity of extending his dominions in a southerly direction. He built fresh fortresses and exacted homage from Count Geoffrey of Mayenne. In 1058 Henry and Count Geoffrey made a final effort to crush their dangerous neighbor; but the effort failed, like those which preceded it. William again allowed the allies to enter and ravage his territory; but, while the French army was crossing the Dive at Varaville, he attacked and completely destroyed their rear-guard, which was cut off from the van by the advancing tide. Henry again made peace, and soon afterward died (1060). The death of Geoffrey of Anjou in the same year relieved William of his most formidable rival for the possession of Maine. Herbert Wake-Dog, the lawful ruler of that territory, who had been dispossessed by Geoffrey, recovered his dominions on the latter's death. He at once "commended" himself to William, thus making the duke his heir. On his death in 1063, William took possession of Le Mans and the county of which it was the capital--an acquisition which extended his southern frontier nearly to the Loire, almost severed Brittany from the rest of France, and paved the way for the subsequent junction with Anjou.