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

It was in the early hours of September 3 that the first definite evidence of Kluck's divergence south-eastward was reported to the Military Government of Paris; but the officers in charge did not venture to disturb their weary chief, who received the news only when he rose in the morning.[51] At noon, he issued to the garrison the following note: "A German army corps, probably the Second, has passed from Senlis southward, but has not pursued its movement toward Paris, and seems to have diverged to the south-east. In a general way, the German forces which were in face of the 6th Army appear to be oriented toward the south-east. On our side, the 6th Army is established to the north-east of the entrenched camp on the front Mareil-en-France–Dammartin–Montgé. The British Army is in the region south of the Marne and the Petit Morin, from Courtevroult (west) to beyond La Ferté-sous–Jouarre (east)."

During the day, the news, the importance of which Gallieni immediately realised, was confirmed; the evening bulletin issued in Bordeaux announced that "the enveloping march of the enemy seems definitely conjured. " Perceiving the opportunity of striking a hard, perhaps a decisive, blow at the enemy's flank, the Governor appears to have resolved at once to set Maunoury's Army in movement,[52] and then to have proceeded to urge the Commander-in-Chief to make this the commencement of the general offensive which was to have taken place some days later, when the armies had re-formed behind the Seine.