The affair at Montmirail was more of a battle than that at Champaubert, for Blücher had been able to gather in the divisions of Sacken, York, Kleist, and Kapzewitch. The battle opened about an hour before noon on the eleventh by a fierce artillery fire from the French, behind which Napoleon manoeuvered so as to concentrate his own force against the Russians, and separate them from York with his Prussians. At two o'clock Napoleon attacked the Russians, Mortier engaging the Prussians separately. The plan succeeded, and by nightfall the enemy was in full retreat for Château-Thierry, where was the nearest bridge over the Marne. Napoleon had hoped that Macdonald would arrive from La Ferté-sous-Jouarre in time to seize the bridge, cut off the retreat, and make the victory decisive. But in spite of heroic exertion, that marshal could not or did not move with sufficient rapidity over the heavy dirt roads. The flying allies sacked the town with awful cruelty, and destroyed the bridge without any molestation except from the inhabitants, who wreaked their vengeance on numerous stragglers. On the thirteenth the French occupied the place, repaired the bridge, and crossed to the right bank. Next morning Marmont started in pursuit of Blücher.
Somewhat flushed by such success, Napoleon deliberated whether he should not now turn and attack Schwarzenberg. The Emperor thought these victories might give pause to a mediocre Austrian, ever mindful of the terrific blows his country had received once and again from France. He was mistaken; Schwarzenberg had moved, though slowly, yet steadily forward. On the twelfth Victor abandoned the bridge at Nogent, and Napoleon sent Macdonald with twelve thousand men to join Victor at Montereau. Early on the fourteenth came news that Blücher had driven Marmont back to Fromentières. By noon Napoleon had effected a junction with this marshal near Étoges, making a famous and successful flank march over a marshy country, a manoeuver which is justly considered worthy of his great genius. Advancing then to the neighborhood of Vauchamps, his infantry attacked in front, while the cavalry, under Grouchy, outflanked the enemy's line and fell on the rear. Blücher was apparently doomed, for he had only three regiments of cavalry, and while facing one powerful enemy he would be forced to break the ranks of another in order to open a line of retreat. He solved the problem, but at enormous cost. Forming his troops into a line of solid squares, one stood to support the artillery and receive the onset in front, while the others dashed at Grouchy's horsemen, each square standing and retreating behind the next alternately as the bloody retreat went on. At last the butchery ceased, and Blücher fled to Bergères. The French pursued only as far as Étoges. Napoleon had hoped to follow all the way to Châlons, annihilate what was left of Blücher's army, and then to return and throw himself on Schwarzenberg. He was arrested by the news that the Seine valley, as far as Montereau, was in the hands of the Austro-Russians; that Oudinot and Victor had been driven back to Nangis; in short, that Paris was seriously menaced.