It would be unnecessary to relate in detail the military operations that now followed in uninterrupted succession. During the first weeks of the new year (1417–18) Henry was active in the field, and though, with the devoutness which so strongly characterised him, he spent Lent in strict retirement, his brothers were busily employed. The great successes of the year were won at Cherbourg and Rouen. Cherbourg was taken by the Duke of Gloucester, aided by a force which the King had ordered to be despatched from some of the western harbours of England. The mere sight of its approach is said to have determined the surrender of the garrison. The siege of Rouen was one of the most important operations of the war, and as it was carried on throughout under Henry’s superintendence it demands a more particular notice. In May the King left Bayeux and marched up the southern bank of the Seine. His first object was to possess himself of the strong position of Pont de l’Arche, situate about eight miles above Rouen, and commonly called the Key of the River. The bridge itself was held by the French in such strength that it could not have been forced without a great sacrifice of men. Henry accordingly marched some three miles lower down the stream to a place where it was divided by an island. The French followed him. While their attention was distracted by a feint (one of the ingenious stratagems with which great commanders are so ready), the island was occupied by a small force of English gunners. A cannonade drove away the troops that had been left to guard the passage, and some thousands of men then crossed without meeting any resistance. Henry now held both banks of the Seine. He constructed a bridge of boats to join his two camps, and in about three weeks’ time received the capitulation of Pont de l’Arche. Leaving a considerable garrison in it, he proceeded to invest Rouen, which was now practically isolated from the rest of France. It was a great, and, considering the strength of the place, even a perilous enterprise. But success would be of inestimable value: the possession of Rouen would mean the acquisition of Normandy.