In these calculations, accurate as far as the information permitted, Buonaparte was greatly misled. He conceived himself to be acting upon the retreat of the allies, and expected only to find a rear-guard at Arcis; he was even talking jocularly of making his father-in-law prisoner during his retreat. If, contrary to his expectation, he should find the enemy, or any considerable part of them, still upon the Aube, it was, from all he had heard, to be supposed his appearance would precipitate their retreat towards the frontier. It has also been asserted, that he expected Maréchal Macdonald to make a corresponding advance from the banks of the Seine to those of the Aube; but the orders had been received too late to admit of the necessary space being traversed so as to arrive on the morning of the day of battle.
Napoleon easily drove before him such bodies of light cavalry, and sharp-shooters, as had been left by the allies, rather for the purpose of reconnoitring than of making serious opposition. He crossed the Aube at Plancey, and moved upwards along the left bank of the river, with Ney's corps, and his whole cavalry, while the infantry of his guard advanced upon the right; his army being thus, according to the French military phrase, _à cheval_ upon the Aube. The town of Arcis had been evacuated by the allies upon his approach, and was occupied by the French on the morning of the 20th March. That town forms the outlet of a sort of defile, where a succession of narrow bridges cross a number of drains, brooks, and streamlets, the feeders of the river Aube, and a bridge in the town crosses the river itself. On the other side of Arcis is a plain, in which some few squadrons of cavalry, resembling a reconnoitring party, were observed manœuvring.
Behind these horse, at a place called Clermont, the Prince Royal of Wirtemberg, whose name has been so often honourably mentioned, was posted with his division, while the elite of the allied army was drawn up on a chain of heights still farther in the rear, called Mesnil la Comtesse. But these forces were not apparent to the vanguard of Napoleon's army. The French cavalry had orders to attack the light troops of the allies; but these were instantly supported by whole regiments, and by cannon, so that the attack was unsuccessful; and the squadrons of the French were repulsed and driven back on Arcis at a moment, when, from the impediments in the town and its environs, the infantry could with difficulty debouche from the town to support them. Napoleon showed, as he always did in extremity, the same heroic courage which he had exhibited at Lodi and Brienne. He drew his sword, threw himself among the broken cavalry, called on them to remember their former victories, and checked the enemy by an impetuous charge, in which he and his staff-officers fought hand to hand with their opponents, so that he was in personal danger from the lance of a Cossack, the thrust of which was averted by his aide-de-camp, Girardin. His Mameluke Rustan fought stoutly by his side, and received a gratuity for his bravery. These desperate exertions afforded time for the infantry to debouche from the town. The Imperial Guards came up, and the combat waxed very warm. The superior numbers of the allies rendered them the assailants on all points. A strongly situated village in front, and somewhat to the left of Arcis, called Grand Torcy, had been occupied by the French. This place was repeatedly and desperately attacked by the allies, but the French made good their position. Arcis itself was set on fire by the shells of the assailants, and night alone separated the combatants, by inducing the allies to desist from the attack.