were extended from Amiens to Verdun, but on September 8, 1914, the German I. Army (General von Kluck) was so placed by the impetuosity of the march that a wide gap separated it from the remainder of the German forces. To the north-west of Paris a new French Army, collected from the Metropolitan garrison and from the south-eastern frontier, had been assembled and pushed out in motor transports by the zeal and intelligence of the Military Governor of Paris (General Gallieni); and to avoid this menace to his flank and line of communications, and to regain touch with the other German armies, one of which (under the Crown Prince) was unsuccessfully engaged in battle, General von Kluck adopted the extremely hazardous course of a flank march, across the front of the Franco-British left wing. Upon receiving intelligence of this manoeuvre from the Air Service in Paris, General Joffre, seeing the opportunity of gaining the initiative, ordered an advance to the attack on September 6, and the First Battle of the Marne, which resulted from this order, changed the character of the fighting on the {29} Western Front. The decisive blow was strategical rather than tactical. It was delivered on a battlefield of 6,000 square miles, and involved, throughout that area, a struggle of six great armies, numbering in all 700,000 troops, against a similar number of armies of at least equal strength. No counter-attack on such a scale had previously been delivered in any campaign, and the scarcely interrupted advance of the German armies received a permanent check, while the strategic aim of the German Staff, namely, the speedy annihilation in the field of the Franco-British armies, had to be definitely abandoned.