World War I, The First Battle of the Marne
Already on September 3, General J.-S. Gallieni, the military governor of Paris, had guessed the significance of the German 1st Army's swing inward to the Marne east of Paris. On September 4 Joffre, convinced by Gallieni's arguments, decisively ordered his whole left wing to turn about from their retreat and to begin a general offensive against the Germans' exposed right flank