This was not the only factor that was framing up to give the German armies a decided advantage. The essential factor of the Aisne was the arrival of General von Zwehl and his guns. On September 13, 1914, at 6 a. m., Zwehl arrived in Laon, and in less than an hour he was in action on the Aisne front. The story of General von Zwehl and his guns is essential to an understanding of the causes that rendered the British victory of the Aisne a barren and a fruitless victory at best. The week of September 5-12, 1914, witnessed the entire series of the battles of the Marne, which drove the Germans across the Marne and across the Aisne, as well as a German victory which exerted almost as powerful an influence in favor of the invaders as the check at the Marne did for the defenders. This victory was the fall of Maubeuge. It is going too far to say--as several military writers have done--that General von Zwehl saved Germany, and that unless he had arrived as opportunely as he did the "German retreat to the Aisne valley would have been changed into a disastrous and overwhelming rout." But it is not going too far to say that the successful holding of the Aisne line was due to the victor of Maubeuge. General von Zwehl was one of the iron-jawed battle-scarred warriors of 1870, a man with a will as metallic as his own siege guns, and a man who could no more be deflected from his purpose than a shell could be diverted in its flight. He had been set to reduce Maubeuge and he had done so with speed and with thoroughness. Maubeuge was not protected by open-air earthworks, but by a circle of armor-plate concrete forts. To the mighty siege guns handled by General von Zwehl, these were no trouble, for Von Zwehl had not only the heavy batteries attached to the Seventh Army Reserve, but he also had a number of Von Kluck's guns and the majority of General von Buelow's, neither of whom was expected to need siege guns in the forward drive where mobility was an essential. In addition to this, General von Zwehl also had the great siege train that had been prepared for the reduction of Paris. What chance had Maubeuge against such a potency?