How did William I gain support from Pope Alexander II for his invasion of England?

To secure support from Pope Alexander II for his invasion of England in 1066, William I petitioned the papacy and leveraged specific diplomatic arguments to justify his cause.1

Key factors in obtaining this support included:

• The Broken Oath: William utilized the claim that Harold II had previously sworn an oath to support William’s claim to the English throne while visiting Normandy, and that Harold had subsequently violated this promise.12
• Ecclesiastical Grievances: The papacy was receptive to William’s cause partly due to resentment over the appointment of Stigand as archbishop of Canterbury, which was viewed as irregular.2
• Papal Reform Interests: Alexander II, influenced by his adviser Archdeacon Hildebrand (the future Pope Gregory VII), saw the invasion as an opportunity to extend the influence of the church reform movement.13

The papacy granted its blessing to the invasion without hearing a defense from Harold’s side. This papal endorsement proved strategically vital, as it provided moral legitimacy for the venture and helped William recruit a diverse army from outside Normandy.21