Castille was a yet more serious danger; and an effort which Edward made to neutralize its attack only forced Henry of Trastamara to fling his whole weight into the struggle. The two daughters of Pedro had remained since their father's flight at Bordeaux. The elder of these was now wedded to John of Gaunt, Edward's fourth son, whom he had created Duke of Lancaster on his previous marriage with Blanche, a daughter of Henry of Lancaster and the heiress of that house, while the younger was wedded to Edward's fifth son, the Earl of Cambridge. Edward's aim was that of raising again the party of King Pedro and giving Henry of Trastamara work to do at home which would hinder his interposition in the war of Guienne. It was with this view that John of Gaunt on his marriage took the title of king of Castille. But no adherent of Pedro's cause stirred in Spain, and Henry replied to the challenge by sending a Spanish fleet to the Channel. A decisive victory which this fleet won over an English convoy off Rochelle proved a fatal blow to the English cause. It wrested from Edward the mastery of the seas, and cut off all communication between England and Guienne. Charles was at once roused to new exertions. Poitou, Saintonge, and the Angoumois yielded to his general Du Guesclin; and Rochelle was surrendered by its citizens in 1372. The next year saw a desperate attempt to restore the fortune of the English arms. A great army under John of Gaunt penetrated into the heart of France. But it found no foe to engage. Charles had forbidden any fighting. "If a storm rages over the land," said the king coolly, "it disperses of itself; and so will it be with the English." Winter in fact overtook the Duke of Lancaster in the mountains of Auvergne, and a mere fragment of his host reached Bordeaux. The failure of this attack was the signal for a general defection, and ere the summer of 1374 had closed the two towns of Bordeaux and Bayonne were all that remained of the English possessions in Southern France. Even these were only saved by the exhaustion of the conquerors. The treasury of Charles was as utterly drained as the treasury of Edward; and the kings were forced to a truce. [Sidenote: The Social Strife]