The cause of the miracle was the doings of the French left wing. Joffre had hurled Maunoury on Kluck’s flank and rear, while Sir John French and Franchet d’Esperey attacked in front. Kluck met the threat with vigour and resolution. He formed front to flank, as the phrase goes—that is, he faced round to what had been his wing—and in the three days’ fighting all but defeated Maunoury. On the night of the 7th the outflanking French left found itself outflanked in turn, and its attack turned into a desperate defence. But on the 9th came salvation. Kluck’s manoeuvre had left a gap of 30 miles between himself and Bülow, and into this gap were pouring the British force and that of Franchet d’Esperey. Suddenly Maunoury discovered that certain villages in front of him were evacuated, and his airmen told him of enemy convoys moving to the north. At 1 p.m. that day Bülow began his retreat, and Kluck was forced to follow suit. Sir John French and Franchet d’Esperey had pierced the enemy front, and the retreat of the German right caused the retreat of all the German armies. They fell back to a line along the Aisne, through Champagne, and down the east bank of the Meuse—a strong line, which for four years was never really broken. But, none the less, it was a retreat. The First Battle of the Marne may well rank as the greatest, because the most critical, contest of the war. It was decisive in the sense that it defeated Germany’s first plan of campaign. She had hoped for a "battle without a morrow"; but the battle had been fought and the morrow was come. She was now compelled to accept the slow war of entrenchments, and to see every week bringing her nearer to the condition of a beleaguered city. The immediate cause of victory was Maunoury’s flank attack, which opened the way for the British and Franchet d’Esperey. But without the daring strategy of Foch and the stubborn endurance of Langle de Gary and Sarrail—above all, without Castelnau’s epic resistance at Nancy—the chance in the West could not have been seized, and the Marne might have realized Germany’s hopes. It was in a sense the last battle of the old régime of war, a battle of movement and surprise and quick decisions; it was fought and won not by the army as a military machine but by the human quality of the soldier. In the last resort the source of victory was the ancient and unconquerable spirit of France. *PART II.* *THE WESTERN FRONT.* *CHAPTER IV.* *THE WORCESTERS AT THE FIRST BATTLE OF YPRES.*