In order that Foch might deliver the blow, it was necessary that Manoury should risk annihilation. Why? That, as Horace saw long afterward, was a part of the great strategical plan of the French High Command under Joffre. The four-day engagement between Manoury and Von Kluck had drained the power of the Sixth French Army to its last gasp, but--it had taken the whole force of Von Kluck's right wing to do it. The British were advancing steadily (though so slowly that it imperiled the whole plan) on Von Kluck's left wing. Manoury and the British, then, like two leeches, were sucking Von Kluck's forces westward, at a time when the German line was driving southeastward. The Fifth Army, under General d'Esperey (who had taken Lanrezac's place when the army was reënforced) was a powerful force, containing six full army corps, three of them fresh reserves. The Germans, believing it to be the same army they had routed at Charleroi, esteemed it lightly. But on Sunday, Monday and Tuesday, it steadily drove Von Buelow back, crossing the Marne and holding the bridgeheads. In this it was helped by the British heavy artillery, an arm in which the French army was weakest. At the same time, d'Esperey's pressure enabled the British advance. There was magnificent fighting here, for Von Buelow was in strength with a full equipment of artillery. The Ninth Army, under General Foch, had suffered heavily. Two German armies opposed it: four army corps under Von Hausen, who was flushed with victory and pursuit, and the independent command of the Prussian Guard, consisting of one entire army corps. Foch had three army corps, nearly all fresh troops, but he would not use them all. Von Hausen and the Prussian Guard attacked savagely and heavily. Foch allowed his line to sag, purposely, to thin the German line, but on Monday he was driven back, and on Tuesday, the German drive was so vicious and powerful, that Foch's right wing was forced back for ten miles. On Wednesday, then, the same day that Von Kluck was encircling Manoury, Von Hausen had all but pierced the French line at Foch's right wing. A bad gap had been formed because Langle de Cary, on the left wing of the Fourth Army, had held firm. There was almost a hole, therefore, ten miles wide, running slantwise behind Langle de Cary's left rear. The Battle of the Marne is the most important victory of modern times. It saved France. In a measure it saved the world. As the victory hangs on a curious battle formation which developed that afternoon of Wednesday, September 9, its main features may be repeated. It is well to see how the various armies stood at midday of this decisive day. At midday, Von Kluck was encircling Manoury, having drawn his right wing far to the north and west to do so. His left wing was in momentary danger of attack from the British, who had crossed the Marne. This wing was being driven north.