At the Emperor's instigation, the Cardinal Infante, the brother of Philip IV. of Spain, and the Viceroy of Milan, had raised an army of 14,000 men, intended to act upon the Rhine, independently of Wallenstein, and to protect Alsace. This force now appeared in Bavaria, under the command of the Duke of Feria, a Spaniard; and, that they might be directly employed against the Swedes, Altringer was ordered to join them with his corps. Upon the first intelligence of their approach, Horn had summoned to his assistance the Palsgrave of Birkenfeld, from the Rhine; and being joined by him at Stockach, boldly advanced to meet the enemy's army of 30,000 men. The latter had taken the route across the Danube into Swabia, where Gustavus Horn came so close upon them, that the two armies were only separated from each other by half a German mile. But, instead of accepting the offer of battle, the Imperialists moved by the Forest towns towards Briesgau and Alsace, where they arrived in time to relieve Breysack, and to arrest the victorious progress of the Rhinegrave, Otto Louis. The latter had, shortly before, taken the Forest towns, and, supported by the Palatine of Birkenfeld, who had liberated the Lower Palatinate and beaten the Duke of Lorraine out of the field, had once more given the superiority to the Swedish arms in that quarter. He was now forced to retire before the superior numbers of the enemy; but Horn and Birkenfeld quickly advanced to his support, and the Imperialists, after a brief triumph, were again expelled from Alsace. The severity of the autumn, in which this hapless retreat had to be conducted, proved fatal to most of the Italians; and their leader, the Duke of Feria, died of grief at the failure of his enterprise. In the mean time, Duke Bernard of Weimar had taken up his position on the Danube, with eighteen regiments of infantry and 140 squadrons of horse, to cover Franconia, and to watch the movements of the Imperial-Bavarian army upon that river. No sooner had Altringer departed, to join the Italians under Feria, than Bernard, profiting by his absence, hastened across the Danube, and with the rapidity of lightning appeared before Ratisbon. The possession of this town would ensure the success of the Swedish designs upon Bavaria and Austria; it would establish them firmly on the Danube, and provide a safe refuge in case of defeat, while it alone could give permanence to their conquests in that quarter. To defend Ratisbon, was the urgent advice which the dying Tilly left to the Elector; and Gustavus Adolphus had lamented it as an irreparable loss, that the Bavarians had anticipated him in taking possession of this place. Indescribable, therefore, was the consternation of Maximilian, when Duke Bernard suddenly appeared before the town, and prepared in earnest to besiege it.