In the meantime, Napoleon being at Rheims, as stated, on the 15th and 16th March, was alarmed by the news of the loss of the battle of Bar, the retreat of the three maréchals beyond the Seine, and the demonstrations of the grand army to cross that river once more. He broke up, as we have seen, from Rheims on the 17th, and sending Ney to take possession of Chalons, marched himself to Epernay, with the purpose of placing himself on the right flank, and in the rear of Schwartzenberg, in case he should advance on the road to Paris. At Epernay, he learned that the allies, alarmed by his movements, had retired to Troyes, and that they were about to retreat upon the Aube, and probably to Langres. He also learned that the maréchals, Macdonald and Oudinot, had resumed their advance so soon as their adversaries began to retreat. He hastened to form a junction with these persevering leaders, and proceeded to ascend the Aube as high as Bar, where he expected to throw himself into Schwartzenberg's rear, having no doubt that his army was retiring from the banks of the Aube. 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.