With a fleet of one thousand five hundred sail Henry crossed the sea and landed without opposition at Chef de Caux, near Harfleur, at the mouth of the Seine. The force that he brought with him was about thirty thousand men, and he immediately employed it in laying siege to Harfleur. The place was strong, so far as walls and bulwarks could make it, but it was not well victualled, and after a five-weeks' siege it was obliged to capitulate. But the forces of the besieged were thinned by disease as well as actual fighting. Dysentery had broken out in the camp, and, though it was only September, they suffered bitterly from the coldness of the nights; so that, when the town had been won and garrisoned, the force available for further operations amounted to less than half the original strength of the invading army. Under the circumstances it was hopeless to expect to do much before the winter set in, and many counselled the King to return to England. But Henry could not tolerate the idea of retreat or even of apparent inaction. He sent a challenge to the Dauphin, offering to refer their differences to single combat; and when no notice was taken of this proposal, he determined to cut his way, if possible, through the country to Calais, along with the remainder of his forces. It was a difficult and hazardous march. Hunger, dysentery, and fever had already reduced the little band to less than nine thousand men, or, as good authorities say, to little more than six thousand. The country people were unfriendly, their supplies were cut off on all sides, and the scanty stock of provisions with which they set out was soon exhausted. For want of bread, many were driven to feed on nuts, while the enemy harassed them upon the way and broke down the bridges in advance of them. On one or two occasions, having repulsed an attack from a garrison town, Henry demanded and obtained from the governor a safe-conduct and a certain quantity of bread and wine, under threat of setting fire to the place if refused. In this manner he and his army gradually approached the river Somme at Blanche Tache, where there was a ford by which King Edward III had crossed before the battle of Crecy. But while yet some distance from it, they received information from a prisoner that the ford was guarded by six thousand fighting men, and, though the intelligence was untrue, it deterred him from attempting the passage. They accordingly turned to the right and went up the river as far as Amiens, but were still unable to cross, till, after following the course of the river about fifty miles farther, they fortunately came upon an undefended ford and passed over before their enemies were aware.