In order to secure the cooperation of all his vassals in his plans for the invasion, Philip denounced John as an enemy of the Church, thereby justifying his attack as motivated solely by religious scruples. He summoned an assembly of French barons at Soissons, which was well attended with the exception of Count Ferdinand of Flanders. Ferdinand refused to attend, still angry over the loss of the towns of Aire and Saint-Omer that had been captured by Philip's son Louis the Lion. He would not participate in any campaign until restored to all ancient lands.