After weighing all the disadvantages on either side, Napoleon determined to turn his arms against Blucher, as most hostile to his person, most rapid in his movements, and most persevering in his purposes. He left Oudinot, Macdonald, and Gerard in front of the grand army, in hopes that, however inferior in numbers, they might be able to impose upon Schwartzenberg a belief that Napoleon was present in person, and thus either induce the Austrian to continue his retreat, or at least prevent him from resuming the offensive. For this purpose the French troops were to move on Bar-sur-Aube, and occupy, if practicable, the heights in that neighbourhood. The soldiers were also to use the cry of _Vive l'Empereur_, as if Napoleon had been present. It was afterwards seen, that as the maréchals did not command 40,000 men in all, including a force under Macdonald, it was impossible for them to discharge effectually the part assigned them. In the meanwhile, Napoleon himself continued his lateral march on Blucher, supposing it possible for him, as formerly, to surprise his flank, as the Prussians marched upon Paris. For this purpose he moved as speedily as possible to La Ferté-Gauchère, where he arrived 1st March; but Sacken and D'Yorck, who would have been the first victims of this manœuvre, as their divisions were on the left bank of the Marne, near to Meaux, crossed the river at La Ferté Jouarre, and formed a junction with Blucher, who now resolved to fall back on the troops of Bulow and Winzengerode. These generals were, it will be remembered, advancing from the frontiers of Belgium. A sudden hard frost rendered the country passable, which had before been in so swampy a condition as to render marching very difficult. This was much to the advantage of the Prussians. Napoleon detached the forces under Marmont and Mortier, whom he had united with his own, to press upon and harass the retreat of the Prussian field-maréchal; while he himself, pushing on by a shorter line, possessed himself of the town of Fismes, about half way betwixt Rheims and Soissons. The occupation of this last place was now a matter of the last consequence. If Blucher should find Soissons open to him, he might cross the Marne, extricate himself from his pursuers without difficulty, and form his junction with the army of the North. But if excluded from this town and bridge, Blucher must have hazarded a battle on the most disadvantageous terms, having Mortier and Marmont on his front, Napoleon on his left flank, and in his rear, a town, with a hostile garrison and a deep river.