Gustavus now made a triumphal march, loved and respected by both Catholics and Protestants, through the garden spot of Germany. After resting his weary troops in the rich district of Wurzburg, he continued his march to Frankfort-on-the-Main, which opened her gates at the first summons. Gustavus crossed the Rhine at Oppenheim and on December 20th he entered Mainz, having cleared the Palatinate of its Spanish garrison. The Elector of Saxony and General Armin invaded Bohemia and occupied Prague. Gustavus now commanded from the Arctic Ocean to the Alps, and from the Rhine to the Moldau. He encamped at Main with an army of twenty thousand men. All the Protestant princes here paid him court. It was his plan to form a Corpus Evangelicum, or Union, under the protection of Sweden, which would include what is now called Germany and all Scandinavia. France was much disconcerted by these Swedish victories. It was all right to curtail the pretensions of the House of Hapsburg, but to the eyes of Richelieu it would be a much worse fate for a new Emperor of Germany to bear the name of Gustavus than to let the Hapsburgs have undue sway. Richelieu now insisted that Gustavus must come to an understanding with the Catholic League of southern Germany. Gustavus refused to surrender his conquests till the League saw that Maximilian of Bavaria, who was the head of the League, was disarmed. Richelieu at that broke his alliance with Gustavus and renewed his alliance with the Emperor. This was quite equivalent to a declaration of war. Richelieu declared himself the protector of the Catholic princes. They again took heart and brought together their armies in behalf of Austria. The Jesuits who were at the Protestant courts succeeded in again stirring up the envy and jealousy of those weak northern Protestant German Electors. The Elector of Saxony now went back in heart, if not in force, to Austria. Gustavus had felt that this would occur, and this was the main reason he had not pushed his triumph to Vienna. He now quickly conquered Franconia. Frankfort-on-the-Main, instead of opening her gates in welcome at his approach, wanted a parley. This city had received special commercial advantages from the Empire, and now they feared if Gustavus were well received they would lose their celebrated fairs. When summoned to surrender they sent a deputation to the King of Sweden explaining these conditions and hoping he would not urge compliance with his demands.