From Boulogne and from other ports the troops were sent up to the wavering line of battle along the Franco-Belgian frontier. They came not to win a victory but to save an army from disaster. The mass of French reserves were in Lorraine or far away to the south, and the safety of the French line on the northern front had depended upon the assumed impregnability of Namur and an equally fallacious underestimate of the number of German troops in Belgium. Three French armies, the Third, the Fourth, and the Fifth, were strung along the frontier from Montmédy across the Meuse and the Sambre to a point north-west of Charleroi, where the British took up their position stretching through Binche, Mons, and along the canal from Mons to Condé. Far away to the south-west was a French Territorial corps in front of Arras, and at Maubeuge behind the British centre was a French cavalry corps under General Sordet. The French staff anticipated a defeat of the German attack on these lines and then a successful offensive, and military critics in England even wrote of the hopeless position of the Germans under Von Buelow and Von Kluck thrust far forward into a cul-de-sac in Belgium with the French on their left at Charleroi, the British on their right front at Mons, and the Belgians on their right rear before Antwerp. The German calculation was that the Belgians had been effectively masked by a corps detached north-westwards from Brussels, that the Duke of Württemberg and Von Hausen had troops enough to force the Meuse, drive in the French right, and threaten the centre at Charleroi, and that Von Buelow could cross the Sambre and Von Kluck encircle the British flank. The strength which the Germans developed in Belgium and the extension of their right wing are said to have been an afterthought due to the intervention of the British Expeditionary Force; but the original German plan required some such modification when the presence of British troops lengthened the line of French defence.