Such was the country over which the battles of the Marne were fought, such were the numbers and dispositions of the several armies on each side, and such, as far as can be judged, were the plans and counterplans of the strategic leaders in the great conflict.
The first movement in this concerted plan was taken by the German extreme right. This was the closing in of General von Kluck's army in a southeasterly direction. It was a hazardous move, for it required General von Kluck to execute a flank march diagonally across the front of the Sixth French Army and the British Expeditionary Force. At this time, according to the dispatches from Sir John French, the British army lay south of the Marne between Lagny and Signy-Signets, defending the passage of the river and blowing up the bridges before General von Kluck.
On September 4, 1914, air reconnaissances showed that General von Kluck had stopped his southward advance upon Paris, and that his columns were moving in a southeasterly direction east of a line drawn through Nanteuil and Lizy on the Ourcq. Meanwhile the French and British generals more effectually concealed their armies in the forests, doing so with such skill that their movements were unmarked by the German air scouts. All that day General von Kluck moved his forces, leaving his heavy artillery with about 100,000 men on the steep eastern bank of the Ourcq and taking 150,000 troops south across the Marne toward La Ferté Gaucher. He crossed the Petit Morin and the Grand Morin, all unconscious that scores of field glasses were trained upon his troops.
Probably believing that the British army had been hurried to the aid of General Sarrail, General von Kluck advanced confidently. Having concealment in view, the commanders of the French army and the British army between them had left a wide gap between the two armies. Through one of these apparently unguarded openings a strong body of uhlan patrols advanced, riding southward until they reached Nogent, south of Paris, and seemingly with the whole rich country of central France laid wide open to a sharp and sudden attack. Among the many strange features of this series of the battles of the Marne this must certainly be reckoned as one. Though possessing an unequaled military organization, though priding itself on its cavalry scouts, though aided by aerial scouts, and though well supplied with spies, yet the Allied armies, with the age-old device of a forest, were able to cloak their movements from this perfectly organized and powerful invading army. Much of the credit of this may be assigned to the French and English aircraft, which kept German scouting aircraft at a distance. But the Allied generals were astounded at the result of their maneuver, which, as they admitted afterward, was merely a military precautionary measure against the discovery of artillery sites, and a device to keep the enemy in general ignorance.