Perhaps the French King was from the first mistaken in his man. Certain it is that when immediately after the marriage he seized St. Omer and Aire, and under pretext of hospitality forcibly detained the newly-married couple, _en route_ for Flanders, at Péronne, until they acquiesced in this act of spoliation, Ferdinand showed no disposition to submit to the outrage tamely. He went forth from his prison at Péronne filled with projects of vengeance, and having concluded a secret treaty with John of England, he waited to see what would happen. For two years he was fain to possess his soul in patience, but everything comes to the man who knows how to wait, and at the expiration of this time Ferdinand's opportunity came. Philip Augustus was now gathering up his strength for a crusade against John, whom the Pope had declared to have forfeited his crown, and he had summoned his vassals to meet him at Soissons. Ferdinand alone refused help. St. Omer and Aire, he averred, must first be restored to Flanders. Philip offered a money equivalent; Ferdinand would not accept it. Nothing but the restitution of the ceded cities would content him. By taking possession of them Philip had violated his duty as lord, and henceforth he (Ferdinand) was in no way bound by his oath of allegiance. 'One of two things must needs come to pass,' King Philip had swore when he learned that Ferdinand had renounced his overlordship; 'France must be Flemish, or Flanders French,' and presently he led into the Netherlands the great army which he had assembled to fight King John, who had now made his peace with the Pope. On May 24 Cassel fell, later on Ghent was invested, by the close of the summer the French were at the gates of Bruges. Soon tottering walls and smouldering embers were all that remained of 'its famous seaport called Damme,' and the vast wealth of merchandise stored there, and thousands of homes had been reduced to ashes. The fertile country round was white to harvest, and Philip reaped it with sickles of flame. From Bruges to the seashore all the country-side was one great field of black stubble. All through the autumn the French King harried Flanders; Lille, Cassel, Courtrai, and a host of smaller towns had shared the fate of Damme before the snows of winter drove him back again to his native land.