The Battle of the Marne by G.H. Perris — Read

In the original design of the whole battle, the action of the right or eastern half of the Allied crescent was to be reciprocal to that of the left -- while the centre held, Sarrail was to strike out from the region of Verdun westward against the flank of the Prince Imperial, as Maunoury struck out eastward from the region of Paris against that of Kluck. Something of this intention came into effect; but it was much modified by two circumstances. In the first place, General Joffre was driven both by major opportunity and by penury of means to make a choice. He decided that Verdun rather than Paris must run the greater risk, that Kluck's headlong advance made the west the chief theatre for his offensive; and, to make sure on the west, he further weakened the eastern armies. It was, then, on terms of something less than equality of numbers that Sarrail and de Langle had to meet the Crown Prince, the IV Army, and the Saxon left, with their greatly superior equipment.

Secondly, the danger beyond the Meuse could not be ignored; and anxiety on this score necessarily handicapped Joffre's plan. The German idea was to cut Verdun off on either side: no direct attack was made upon the fortress, the Crown Prince proceeding around the entrenched camp by the west, while the Lorraine armies approached on the east and the IV Army swept over the empty flats of Champagne. On September 5, the German V Army, coming down both sides of the Argonne, had reached the open country south of the forest of Belnoue, that is, from 20 to 30 miles south-west of Verdun. It was, doubtless, expected that the Meuse fortress would be abandoned, as, indeed, it must have been had the French retreat continued longer.