Late in December 1915, the possibility of an attack on Verdun was brought to the attention of General Gallieni, French Prime Minister of War. On 16 December 1915, he queried Marshal Joffre, Group Commander of the French First and Second Armies, as to whether a two line defensive system, to include all necessary construction, had been planned and completed. Joffre replied that on 22 October he had ordered the improvement along the entire front of the existing double line defense system and the organization of the fortified areas in the rear of the lines. These defensive measures were nearing completion and at a number of points were completed.
At this time, Joffre was centering his thoughts much more on the plans for the coordinated Allied offensive along the Somme slated for July 1916, than on the defense of the Verdun. In fact, since August 1915, when he assumed control of the fortress of Verdun, Joffre had been draining it of its men and guns without taking any measures to compensate for the losses with more adequate trench defenses. Privately, he felt the "apprehensions of an attack on Verdun were baseless," despite reports from his Intelligence Branch of German activities near Verdun. Such rumors, he thought, were "calculated to disturb profoundly the spirit of discipline in the Army". Similarly, his Operations Staff was too concerned with the offensive schedules for the July offensive to pay heed. As late as 18 February in a letter to General Haig, British Commander-In-Chief, Joffre stated that if the Germans took the offensive at all, it would be against the Russians.
On 10 February 1916, the garrison under General Herr consisted of seven divisions and two territorial brigades in the line, with one division in reserve. These forces were deployed for the defense of the area between the Second Army in the Argonne and the First Army in Woevre. They occupied a series of four defensive parallel lines of which only one was fully manned. Reports of German activities in front of the Verdun area led General Herr to request additional troops for a speedy concentration of forces in the Verdun defense. As a result of this request, six divisions were diverted from the Somme and arrived at the Verdun Forts on 20 February, one day before the German attack.
At this time, the logistical problems to support the Verdun forces were critical. Of the two standard gauge railroads serving Verdun, one to the south was cut off above St-Mihiel and other to the west was within easy range of the German artillery. All that remained was the Meusian Railroad Line with a carrying capacity of 800 tons per day and the road from Bar-le-Duc to Verdun to transport men and material for the gigantic struggle. Marshal Petain, who shortly after the attack assumed command of the Verdun defense, initiated the day and night motor convoys that hauled ammunition, food supplies, guns and personnel to the front. By March 1916, 3,500 vehicles were streaming back and forth over this seven yard wide route, at times reaching a rate of one vehicle every five seconds, to serve the defensive troops. This roadway between Bar-le-Duc and Verdun is now known as the "Voie Sacree" (Sacred Way) and is lined with special Voie Sacree "milestones". See Picture Below
In planning the offensive, Falkenhayn scheduled his attack for 13 February. Heavy rains and haze over the battlefield made him postpone the attack to the 21st of February. This delay permitted the French to move up the reserves to almost double General Herr's forces and prevent what might have been a severe defeat and breakthrough by the German forces.
For the offensive, Crown Prince Rupprecht, Commander of the German forces, had twenty six divisions, of which a third was held in general reserves. The plan proposed using nine divisions in a penetration of the stronghold in the plain of Woevre, which were ready to assault the French flank as soon as the front was breached. Four more divisions, deployed on the west bank of the Meuse north of Verdun, had orders to attack the French to bar any French retreat when the breach on the eastern side was accomplished.