Von Kluck and Von Buelow had not reached their advanced positions easily. They had been severely mauled in two defeats, at Le Cateau and at Guise. In a war of less magnitude, these would have appeared as great Allied victories, but Joffre preferred to lose the advantage of following up these victories for the greater advantage of falling back strategically in good order. Moreover, the forts of Maubeuge still held. It was not until the grim old warrior Von Zwehl, with superhuman energy, brought up the great siege-guns, that Maubeuge fell. It was then too late for the guns to be of any service in the Battle of the Marne. That Saturday afternoon, learning from air scouts that Von Kluck had massed his forces to the south, in order to attack the British on the morrow and pierce the gap, Manoury determined to force the issue. He launched his small and war-wearied army against the reserve which Von Kluck had left behind to guard the crossing of the Ourcq. The western end of the Battles of the Marne had begun. Two important results developed immediately. One was Manoury's discomfiting discovery that the German heavy artillery gave the invaders a tremendous advantage when great mobility was not needed, as, for example, in defense of the crossings of a stream. The other was Von Kluck's discomfiting discovery that Manoury's army, attacking his reserves, was far stronger in fighting power than he thought. Each of these surprises counterbalanced the other. This same Saturday afternoon, moreover, at the time that Manoury attacked, Von Kluck, from the other wing of his army, had sent a scouting party of cavalry to find out the location of the British Army. It was an excellent opportunity to cut them up, but the British Field Marshal had drawn his troops into cover of the forests and he let the scouts go by. A courier, detached from time to time, took to Von Kluck the welcome news that the British were nowhere to be seen and that the hoped-for gap existed. The British chuckled with glee. Von Kluck, surer every moment of flanking the Fifth French Army, hurried his men southward. Suddenly, however, that Saturday evening, Von Kluck received word of the Manoury attack and realized that his reserves were threatened and his own flank was in danger. His men had marched all day. A large section of his army had to march back all night to reënforce the reserves attacked by Manoury.