This is the order of battle for the French Army on the outbreak of war in August 1914.
Background
In 1914, the French War strategy was based on the offensive Plan XVII, which aimed to attack in Alsace-Lorraine. Therefore, the right wing of the French Army was stronger than the left wing.
Order of battle
1) First Army, commanded by Auguste Dubail
Concentration zone : between Remiremont and Charmes
Mission : attack towards Mulhouse and Sarrebourg
Strength : 5 Corps. 266,452 men
2) Second Army, commanded by Édouard de Castelnau
Concentration zone : between Pont-Saint-Vincent and Neufchâteau, Vosges
Mission : attack towards Morhange
Strength : 5 Corps. 323,445 men
3) Third Army, commanded by Pierre Ruffey
Concentration zone : between Saint-Mihiel and Verdun
Mission : Hold the Germans in their defensive positions before Metz
Strength : 3 Corps. 237,257 men
4) Fourth Army, commanded by Fernand de Langle de Cary
Concentration zone : between Saint-Dizier and Bar-le-Duc
Mission : In reserve in the Argonne Region
Strength : 3 Corps. 159,588 men
5) Fifth Army, commanded by Charles Lanrezac
Concentration zone : between Hirson and Dun-sur-Meuse
Mission : Guard the Southern part of the border with Belgium
Strength : 5 Corps. 299,350 men
6) Cavalry Corps, commanded by André Sordet
Concentration zone : around Mézières
Mission : Advance into the Belgian Ardennes in case of a German attack on Belgium. Strength : 15,750 men