That evening, Foch conceived a manœuvre so characteristic of the man, so evidently after his own heart, that the facts of its execution have been hidden under a mass of sparkling fable. “If, by whatever mental vision,” the master had said in one of his lectures, “we see a fissure in a dam of the defence, or a point of insufficient resistance, and if we are able to join to the regular and methodical action of the flood the effect of a blow with a ram capable of breaking the dam at a certain place, the equilibrium is destroyed, the mass hurls itself through the breach, and overwhelms all obstacles. Let us seek that place of weakness. That is the battle of manœuvre. The defence, overthrown at one point, collapses everywhere. The barrier pierced, everything crumbles.” That it was Foch, not Bülow, who had been on the defensive makes no difference: Foch never thought of war in pure defensive terms. Now he saw his opportunity. There was no subtlety in the object. A rush which fails to produce a complete breach opens a flank plainly inviting attack; and the Staff at Plancy had had its eyes fixed all day upon the new German flank, 6 miles long, from Mont Août to Corroy. Twice the 9th Corps had struck at it without success. The boldness of Foch’s design lay, not in its objective, which was evident, but in the means proposed for its execution. The right of the 9th Corps could do no more; its left, the Moroccan Division, had lost the south bank of the marshes, and was hard put to it to hold the hills around Mondemont. Nothing remained but the 42nd Division, which, though greatly fatigued, was in somewhat better posture about Soisy. Two demands now competed in the mind of the French commander. He regarded Mondemont as a key-position to be defended at all costs; and the removal of Grossetti, without compensation, would gravely endanger it. But more than in any position he believed in forcing a result by a well-directed blow when the enemy offered the chance. D’Espérey’s 10th Corps, it is true, had before it the chance of breaking across Bülow’s communications at St. Prix and Baye; it had otherwise no pressing call to make such a movement. Farther south, there were both need and opportunity——the need of relieving the 9th and 11th Corps, the opportunity of a decisive action. Grossetti, then, must come to Linthes, and d’Espérey’s 51st Division, in reserve of the 10th Corps, must take his place west of Mondemont. D’Espérey’s loyalty in agreeing to this arrangement cannot be too warmly praised. The comradeship of arms, so influential a factor in the victory of the Marne, was nowhere more admirably illustrated.