The stretch of river which confronted the British Army when they set about the hazardous crossing of the Aisne was about fifteen miles in length. It lay as nearly as possible east and west, so that the advance was from south to north. As the British faced the river the First Army Corps was on the right of their line, together with half the cavalry. In the centre was the Second Corps, on the left the Third Corps, which was still without one of its divisions (the Sixth), but retained, on the other hand, the 19th Brigade, which did not belong to it. Each of these British corps covered a front of, roughly, five miles. Across the broad and swift river a considerable German army with a powerful artillery was waiting to dispute the passage. On the right of the British were the French Fifth and Seventh Armies, and on their left, forming the extremity of the Allied line, was the French Sixth Army, acting in such close co-operation {163} with the British Third Corps in the Soissons region that their guns were often turned upon the same point. This Sixth French Army, with the British Army, may be looked upon as the left wing of the huge Allied line which stretched away with many a curve and bend to the Swiss frontier. During all this hurried retreat from the Marne, it is to be remembered that the Eastern German armies had hardly moved at all. It was their four armies of the right which had swung back like a closing door, the Crown Prince's Fifth Army being the hinge upon which it turned. Now the door had ceased to swing, and one solid barrier presented itself to the Allies. It is probable that the German preponderance of numbers was, for the moment, much lessened or even had ceased to exist, for the losses in battle, the detachments for Russia, and the operations in Belgium had all combined to deplete the German ranks. The Belgian Army had retired into Antwerp before the fall of Brussels, but they were by no means a force to be disregarded, being fired by that sense of intolerable wrong which is the most formidable stimulant to a virile nation. From the shelter of the Antwerp entrenchments they continually buzzed out against the German lines of communication, and although they were usually beaten back, and were finally pent in, they still added to the great debt of gratitude which the Allies already owed them by holding up a considerable body, two army corps at least, of good troops. On the other hand, the fortress of Maubeuge, on the northern French frontier, which had been invested within a few days of the battle of Mons, had now fallen before the heavy German guns, with the result that at least a corps of troops under {164} Von Zwehl and these same masterful guns were now released for service on the Aisne. [Sidenote: Wonderful work of the sappers.]