January 1814) Napoleon surprised Blücher at his headquarters and nearly captured him. Having learnt that Napoleon was at hand Blücher fell back a few miles to the east the next morning to a strong position covering the exits from the Bar-sur-Aube defile. There he was joined by the Austrian advance guard and together they decided to accept battle—indeed they had no alternative, as the roads in rear were so choked with traffic that retreat was out of the question. At about noon on 2 February Napoleon attacked them opening the Battle of La Rothière. The weather was terrible, and the ground so heavy that the French guns, the mainstay of Napoleon's whole system of warfare, were useless and in the drifts of snow which at intervals swept across the field, the columns lost their direction and many were severely handled by the Cossacks. Although the French inflicted more damage than they received, Napoleon retired to Lesmont, and from there to Troyes, Marshal Marmont being left to observe the enemy. Owing to the state of the roads, or perhaps to the extraordinary lethargy which always characterized Schwarzenberg's headquarters, no pursuit was attempted. But on 4 February Blücher, chafing at this inaction, obtained the permission of his own sovereign, King Frederick III Prussia, to transfer his line of operations to the valley of the Marne; Pahlen's corps of Cossacks were assigned to him to cover his left and maintain communication with the Austrians. Believing himself secure behind this screen, Blücher advanced from Vitry along the roads leading down the valley of the Marne, with his columns widely separated for convenience of subsistence and shelter the latter being almost essential in the terrible weather prevailing. Blücher himself on the night of 7/8 February was at Sézanne, on the exposed flank so as to be nearer to his sources of intelligence, and the rest of his army were distributed in four small corps at or near Épernay, Montmirail and Étoges; reinforcements also were on their way to join him and were then about Vitry. In the night Blücher's headquarters were again surprised, and Blücher learnt that Napoleon himself with his main body was in full march to fall on his scattered detachments. At the same time he heard that Pahlen's Cossacks had been withdrawn forty-eight hours previously, thus completely exposing his flank. He himself retreated towards Étoges endeavouring to rally his scattered detachments. Campaign