With the appearance on the southern horizon of the fortress of Verdun and the city of Paris, and the entry of the Allied armies between them as into a corridor, the whole problem, in fact, was transformed. The German Command suddenly found itself in face of a fatal dilemma. As Paris obstructed the way of Kluck, so Verdun challenged the Prussian Crown Prince. To enter the corridor without first reducing these two unknown quantities would be to risk serious trouble on both flanks; to stay to reduce them would involve delay, or dispersal of force, either of which would be disastrous. The course of argument by which the Grand Staff decided this deadly question has not been revealed. They chose the first alternative. Kluck was ordered to pass south-eastward of the one “entrenched camp,” the Imperial Crown Prince south-westward of the other, both, and the three armies between them, to overtake the Allies and force them to a frontal encounter, while a fresh effort was made to break through the eastern defences. A heavy price must be paid for such large re-establishments and changes of plan in face of an alert enemy. Kluck has been too much blamed for what followed. He may have been guilty of recklessness, over-reaching ambition, and specific disobedience. But here, as in the Battle of the Frontiers, it is the authors, not the executants, of the offensive operation who must be held chiefly responsible for consequences that are in the logic of the case. Joffre’s hour had come. He had laboured to win three elements of an equal struggle lacking in the north: (_a_) a more favourable balance of numbers and armament——this was gained by the “wearing down” of the enemy, and the reinforcement of the Allied line, in course of the retreat, so that the battle of the Marne commenced with something more than an equality, and ended with a distinct Allied superiority in the area of decision; (_b_) a favourable terrain——this was reached on the classic ground between the capital and the middle Meuse, under cover of the eastern armies, and subject to the dilemma of Paris–Verdun; (_c_) a sound strategic initiative. For this, the 6th Army had been prepared, and the 5th kept at full strength. The failure of the enveloping movement and the change of the German plan provided the opportunity. To reduce the distended front of the invasion, at one time no less than 140 miles (Amiens to Dun-sur-Meuse), to one of 100 miles (Crécy-en-Brie to Revigny), Kluck had boldly crossed the face of the 6th Army, and on the evening of September 5 presented a moving flank of more than 40 miles long to Maunoury, French, and d’Espérey’s left. Joffre seems to have hesitated for a moment as to whether it were best to continue the retreat, as arranged, to the Seine, and then to have given way to Gallieni’s importunity. “We cannot count on better conditions for our offensive,” he told the Government.