Whatever trepidation of heart the Emperor may have felt at these advances, he put on a bold front at Vienna and scoffed at the name of Gustavus Adolphus, declaring that the "Snow King of the North" would soon melt away with his army as he moved southward, but it is a curious fact that people of northern climates can accustom themselves to any latitude, while people born under a hot sun cannot always endure cold, and the Swedes proved that they could fight in any land. The Emperor's confidence was by no means shared by the Catholic League. They now placed General Tilly, who, it was claimed, had never lost a battle, at the head of the Imperial forces. Since Wallenstein had been retired great companies of mercenary soldiers could be had by any commander who could pay them. If Gustavus had possessed money many of these would much have preferred to fight for him. But God was to show, as in the case of Gideon, what could be done with the few. In spite of his faith, however, Gustavus sometimes feared the future. The winter used up most of the food and the money. In a letter to Oxenstiern dated December, 1630, he says: "May God, into whose hands I commit all, help us to live through the winter. Then, thanks to your care and foresight, the summer will be more prosperous. I would like to describe our condition to you, but a sabre cut having rendered my hand stiff, I am prevented from doing so." Let it suffice you to know that the enemy enjoys every advantage for establishing his winter quarters, since all Germany has become his prey. If I had more soldiers with me on the bank of the Oder I would march forward. Although our cause is good and just the issue is uncertain—uncertain are also man's days. "Therefore, I pray you for Christ's sake, be not discouraged if all does not succeed to our wishes. I most earnestly recommend my family to your care if misfortune befall me. It is in many respects worthy of interest. The mother needs advice, she is none too wise. The daughter, a tender child, will be exposed to many difficulties if she should reign, and to many dangers if others should reign over her. I commit both of them, their future, my life and all that I possess in this world, to God's holy and powerful keeping. I am persuaded that whatever may befall me on this earth will always be for my good, and after this life I hope to enjoy eternal peace and joy." Gustavus Adolphus did not remain inactive, but after conquering Pomerania he advanced into the Duchy of Brandenburg, for the purpose of reaching Mecklenburg. He pushed the Imperial troops from Pomerania, so that Tilly fell back to the Elbe, without venturing to defend Frankfort-on-the-Oder, which the Swedes successfully assaulted in a three-days siege about the middle of the winter. William of Hesse-Cassel in October, 1630, gladdened the heart of the king by entering into an alliance with him. Aside from this one prince, not one evangelical prince would come to his assistance.