To give effect to his sentence, Philip invaded Normandy and began to lay siege to its fortresses. John crossed to Normandy, but did not take the field; his conduct was so strange that men thought that some infatuation from heaven had fallen upon him as a judgment for having slain his nephew. He lay at Rouen for many months, giving great feasts, and boasting that when he chose he would drive King Philip out of the duchy. But, instead of sallying out to make his vaunts good, he quietly looked on, while Philip took town after town with little resistance. The Normans did not love John, and fought feebly or not at all. Only Château Gaillard, a great castle which Richard I. had built to guard the valley of the lower Seine, made any serious defence. Instead of opposing the enemy, John fled from Normandy and took refuge in England. After his departure, Rouen and the remaining cities of the duchy threw open their gates to the French. In the following year Philip pursued his victorious career, and completed the conquest of Anjou and Touraine. In 1206 he fell upon Aquitaine, and conquered Poitou and Northern Guienne. Only the great ports of Bordeaux and La Rochelle, with the southern half of Guienne, remained true to John. Thus passed away, not only the great but ephemeral continental empire which Henry II. had built up, but also the Norman duchy itself, whose fortunes had been united to those of England for nearly a century and a half. For the future the Plantagenet kings owned only a corner of southern France, and were no longer great continental sovereigns. The monarch's loss was the nation's gain. England's kings were no longer foreigners; they did not spend half their time abroad, or devote their whole energy to schemes of aggrandisement in France. The Anglo-Norman barons, too, were compelled to become wholly English, since their estates over-sea fell into the hands of the enemy and passed away from them. In this way John's cruelty and shiftlessness did more for England's good than the wisdom and strength of his father. But in the mean while John, being deprived of his continental dominions, was constrained to reside in England, and proved a most undesirable neighbour to his unhappy subjects. After an unsuccessful attempt to reconquer Poitou in 1206, he made peace with King Philip, on such terms as he could obtain. Bordeaux and the duchy of Guienne remained with him, but he was compelled to acquiesce in the loss of all his other provinces. [Sidenote: =Quarrel with Innocent III.--Stephen Langton.=]