For that purpose the allied armies were not posted directly on the front of the German armies, but between them. Consequently the left of one German army and the right of another was attacked by the same French army. In that way two German Generals would have to resist an attack directed by one French General, and every German General would have to resist two independent French attacks. Hence, too, if a German army was forced back the French could at once double round the flank of the German army next in the line if that army was still standing its ground. Choice of the battle ground and command of the roads leading to it ensured that this would happen. As a fact, it did. Finally, all the way behind the French line ran the great road leading across the plateaux from Paris to the fortified frontier. This, with railway communication, gave the needed facilities for the movement of reserves and the transport of munitions and food supplies. Now let us glance at the tactical scheme on the German side. The fact that General von Kluck had left two out of the five corps forming his army on the Ourcq, and was covering his movement to the south of the Marne with his cavalry, proves that he did not, as was supposed, intend to lose contact with Paris. His scheme was to establish an echelon of troops from the Ourcq to La Ferté Gaucher on the great eastern road, believing that to be meanwhile a quite sufficient defence. With the rest of his force he was to join with von Bülow and von Hausen in smashing through the French position at Sezanne. Against that position there was to be the overwhelming concentration of ten army corps. To assist the stroke against Sezanne there was a concurrent intention to break the French line at Vitry-le-François. The French line between Sezanne and Vitry-le-François would then be swept away. Assuming the success of these operations, the German forces would be echeloned south-east from the Ourcq across the valley of the Marne and the plateau south of it to Troyes on the Aube. The Germans would then be in a position to attack in flank the French retreating from the frontier, and ready, when these French troops fell back, pursued by the armies of the Crown Princes of Germany and Bavaria and by von Heeringen's army of the Vosges, to join in the great sweep along the valley of the Seine and round to the south of Paris. By this time, remember, the long lines of communication through Belgium would have ceased to be vital. It was a bold scheme. There are, however, other factors to be taken into account besides tactical plans.