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 some time 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 without incident, it was probably secured earlier. Papal sanction of the marriage appears to have required the founding of two monasteries in Caen – one by William and one by Matilda. The marriage was important in bolstering William's status, as Flanders was one of the more powerful French territories, with ties to the French royal house and to the German emperors. Contemporary writers considered the marriage, which produced four sons and five or six daughters, to be a success.