family and compel them to act consistently with Norman interests. However, in 1052 the king and Geoffrey Martel made common cause against William at the same time as some Norman nobles began to contest William's increasing power. Henry's about-face was probably motivated by a desire to retain dominance over Normandy, which was now threatened by William's growing mastery of his duchy. William was engaged in military actions against his own nobles throughout 1053, as well as with the new Archbishop of Rouen, Mauger. In February 1054 the king and the Norman rebels launched a double invasion of the duchy. Henry led the main thrust through the county of Évreux, while the other wing, under the king's brother Odo, invaded eastern Normandy. William met the invasion by dividing his forces into two groups. The first, which he led, faced Henry. The second, which included some who became William's firm supporters, such as Robert, Count of Eu, Walter Giffard, Roger of Mortemer, and William de Warenne, faced the other invading force. This second force defeated the invaders at the Battle of Mortemer. In addition to ending both invasions, the battle allowed the duke's ecclesiastical supporters to depose Archbishop Mauger. Mortemer thus marked another turning point in William's growing control of the duchy, although his conflict with the French king and the Count of Anjou continued until 1060. Henry and Geoffrey led another invasion of Normandy in 1057 but were defeated by William at the Battle of Varaville. This was the last invasion of Normandy during William's lifetime. In 1058, William invaded the County of Dreux and took Tillières-sur-Avre and Thimert. Henry attempted to dislodge William, but the siege of Thimert dragged on for two years until Henry's death. The deaths of Count Geoffrey and the king in 1060 cemented the shift in the balance of power towards William. One factor in William's favour was his marriage to Matilda of Flanders, the daughter of Count Baldwin V of Flanders. The union was arranged in 1049, but Pope Leo IX forbade the marriage at the Council of Rheims in October 1049. The marriage nevertheless went ahead sometime in the early 1050s, possibly unsanctioned by the pope. According to a late source not generally considered to be reliable, papal sanction was not secured until 1059, but as papal-Norman relations in the 1050s were generally good, and Norman clergy were able to visit Rome in 1050