194 The Great War Germany, through Luxemburg one trunk railroad descended into France by Mezieres and Rethel, a second followed the Meuse Valley from Namur and reached Laon, a third came south from Maubeuge, that is from the main Liege-Paris line to the same town, a fourth, the main line from Paris to Brus- sels, came south through Mons to St. Quentin, Tergnier, to Noyon. Finally in the rear the trunk line from Calais to Switzerland crossed these four railways and made it simple, not merely to direct re- enforcements from one flank to another, but to move troops by Metz and Thionville, from Alsace- Lorraine. Such then was the position to which the Germans had come back on September 13. If they were driven beyond it there remained no satisfactory posi- tion south of the frontier. To lose this foothold they now retained on the second line of the defenses of the French capital was to concede the failure of their whole gigantic offensive. The defeat at the Marne had been officially described at Berlin as a mere change of position for " strategic reasons." The advance had outrun the supplies, but there had been no reverse, so the German General Staff in- sisted. But if the Champagne Hills were retaken by the French no such claim could be made. They would become a barrier to all future invasion and the siege of Paris would have to be begun, if at all, almost a hundred miles from the capital. The Germans had passed this line three weeks