The Allied Generalissimo was forced to give way before the fury of the German onslaught in Belgium. He withdrew his armies while there was yet time, thus averting irrevocable disaster. According to all the rules of the game, he should have retired his whole line southwards, in order to ensure the safety of Paris. But he did not throw his highest trump: he clung to Verdun, and left Paris exposed. His armies retreated, not on the Capital, but in a sweeping movement that was hinged upon Verdun. He realised that the fate of Paris depended not upon its being covered by the Allies, but upon the fate of the second great battle of the war. Meanwhile, the great retreat--this hinging movement--continued, very slowly near Verdun, very, very swiftly on the left. Days passed; no attempt was made to check the enemy's advance, and the passing of each day left Paris more exposed. The world gasped at the breathless swiftness with which disaster seemed to be swooping down upon the Capital. But every day de Castlenau was consolidating his defence of Verdun, in face of tremendous odds; and every day the ferocity of the German onrush waned. The line continued to swing resolutely back, until such time as a completed mobilisation should allow the Allies to turn upon the enemy in greater force, in their own time, and on chosen ground. A premature effort would have spoiled all. They had to wait for their chance. Meanwhile, rapid concentrations of reserves were taking place behind the line, the most famous instance of which was the Reserve Army moved out of Paris by General Gallieni in taxis, fiacres, and any vehicle the authorities could commandeer to ensure that the Army should be in its place in time. It was in its place. Just as the world was beginning to say that the war was over, General Joffre decided that the iron was hot, that the time to strike had arrived. "The moment has come," he wrote, "to die where you stand, rather than give way." The outlook changed from black to rose with the completeness and ease of a pantomime transformation scene. The Verdun heights remained impregnable. The whole line turned and fought where it stood. The enemy, worn out by his exertions, stretched his line of communications to breaking-point, and it was said that his supplies of food and munitions had come temporarily very near to collapse. The Allies checked him. He could not even hold his own. In two days he was moving back, away from Paris.