Meanwhile at Châlons there had been formed a French army of 166 battalions, 100 squadrons, and 380 guns, consisting of the Ist, Vth, VIIth, and XIIth Corps.
Of the last the Division which had been left behind on the Spanish frontier formed the nucleus, to which was added a body of very superior troops, consisting of four regiments of marines; later the two cavalry divisions also joined. General Trochu, who had been made Governor of Paris, had taken back with him thither eighteen battalions of Gardes-Mobiles, they having already given such proofs of insubordination that it was thought unsafe to confront them with the enemy.
The Emperor had arrived in Châlons and had placed Marshal MacMahon in command of the newly-formed army. In the French Head-quarter it was not unnaturally assumed that Marshal Bazaine was in retreat from Metz. By an advance of the Army of Châlons merely to Verdun the armies could form a junction with each other in the course of a few days, and so a fighting force be formed which might make head against the hitherto victorious enemy. On the other hand, MacMahon had to concern himself with the duty of covering Paris, and that capital, no less than his own right flank, was threatened by the appearance of the Crown Prince of Prussia's army on the Meuse.
For the attainment of a decision between advancing and retiring, it was beyond everything necessary to know the direction which Marshal Bazaine might have taken.
On the 18th tidings had come from him, that he had maintained his position in a battle about Rezonville, but that his troops had to be supplied with ammunition and supplies before they could renew the march. From this it seemed only too probable that the communications of the Army of the Rhine were already threatened; and MacMahon determined to march on Rheims, whence he could either reach Paris, though by a somewhat circuitous route, or move in the direction of the other army.
But when it became known that the Crown Prince of Prussia's army had not even been near Metz, and that Prussian cavalry had already appeared before Vitry, the Marshal could not deceive himself as to the danger involved in the latter alternative. With sound judgment, therefore, he stood out against the order of the Empress and the Ministry to undertake that enterprise; he determined against it, and announced his resolution to march to Paris. Under its walls he could accept a battle with advantage, since the fortifications, even in the event of defeat, assured a safe retreat and precluded pursuit.