Banner undertook this bold enterprise. His military reputation had suffered by his last retreat from Bohemia, and it stood in need of some great exploit to restore its former lustre. Without communicating his designs to any one, in the depth of the winter of 1641, as soon as the roads and rivers were frozen, he broke up from his quarters in Lunenburg. Accompanied by Marshal Guebriant, who commanded the armies of France and Weimar, he took the route towards the Danube, through Thuringia and Vogtland, and appeared before Ratisbon, ere the Diet could be apprised of his approach. The consternation of the assembly was indescribable; and, in the first alarm, the deputies prepared for flight. The Emperor alone declared that he would not leave the town, and encouraged the rest by his example. Unfortunately for the Swedes, a thaw came on, which broke up the ice upon the Danube, so that it was no longer passable on foot, while no boats could cross it, on account of the quantities of ice which were swept down by the current. In order to perform something, and to humble the pride of the Emperor, Banner discourteously fired 500 cannon shots into the town, which, however, did little mischief. Baffled in his designs, he resolved to penetrate farther into Bavaria, and the defenceless province of Moravia, where a rich booty and comfortable quarters awaited his troops. Guebriant, however, began to fear that the purpose of the Swedes was to draw the army of Bernard away from the Rhine, and to cut off its communication with France, till it should be either entirely won over, or incapacitated from acting independently. He therefore separated from Banner to return to the Maine; and the latter was exposed to the whole force of the Imperialists, which had been secretly drawn together between Ratisbon and Ingoldstadt, and was on its march against him. It was now time to think of a rapid retreat, which, having to be effected in the face of an army superior in cavalry, and betwixt woods and rivers, through a country entirely hostile, appeared almost impracticable. He hastily retired towards the Forest, intending to penetrate through Bohemia into Saxony; but he was obliged to sacrifice three regiments at Neuburg. These with a truly Spartan courage, defended themselves for four days behind an old wall, and gained time for Banner to escape. He retreated by Egra to Annaberg; Piccolomini took a shorter route in pursuit, by Schlakenwald; and Banner succeeded, only by a single half hour, in clearing the Pass of Prisnitz, and saving his whole army from the Imperialists. At Zwickau he was again joined by Guebriant; and both generals directed their march towards Halberstadt, after in vain attempting to defend the Saal, and to prevent the passage of the Imperialists.