If, consequently, the invading forces could seize and hold these routes and railways, and, as a result, which would to all intents follow, could seize and hold the great main routes and the railways running eastward through the valley of the Seine from Paris to Belfort, the fortified frontier--the key to the whole situation--would in military phrase, be completely "turned." Its defence consequently would have to be abandoned. Not only must its defence have been abandoned, with the effect of giving freedom of movement to the German echelon, but, that barrier removed, the German armies would no longer be dependent for munitions and supplies on the route through Belgium. They could receive them just as conveniently by the route through Metz. Their facilities of supply would be doubled. It will be seen, therefore, to what an extent the whole course of the war hung upon this great clash of arms on the Marne. German success must have affected the future of operations alike in the western theatre and in the eastern. But there is another feature of the roads in the valley of the Marne which is of consequence. Great roads converge into it from the north. Sezanne has already been mentioned. It is half-way along the broad backbone dividing the valley of the Marne from the valley of the Seine. Five great roads meet there from La Ferté-sous-Jouarre, Soissons, Rheims, Chalons, Verdun, and Nancy. Hence the facility for massing at that place a huge body of troops. It will be seen, therefore, that in making Sezanne the point at which they aimed their main blow at the whole French scheme of defence, the Germans had selected the spot where the blow would, in all probability, be at once decisive and possibly fatal. Clearly they had now grasped, at all events in its main intention, the strategy of the French general. _They saw that he was using the fortified frontier to checkmate their Belgian plan._ Summing up the consequences, had success attended the stroke we find that it would have: Opened to the invaders the valley of the Seine. Turned the defence of the fortified frontier. Released the whole of the German armies. Given them additional, as well as safer, lines of supply from Germany. Enabled the German armies to sweep westward along the valley of the Seine, enveloping or threatening to envelop the greater part of the French forces in the field. CHAPTER IV THE BATTLE OF THE MARNE Why, then, if it was so necessary and the object of it so important, was the move begun by General von Kluck on September 3 a false move? It was a false move because he ought to have stood against the forces opposed to him. The defeat of those forces was necessary before the attack against Sezanne could be successful. Conversely, his own defeat involved failure of the great enterprise.