German patriotic feeling was against Gustavus. It was clear that he would have to make his way by the sword, and the sword alone. At the end of March the campaign began. Tilly suddenly dashed at Neu Brandenburg, captured it on March 29th, and destroyed its garrison of 2000 Swedes, thus thrusting himself in between Gustavus in Pomerania and Horn in Mecklenburg. Gustavus saw the danger. By forced marches he succeeded in circumventing Tilly and effecting his junction with Horn, and the old marshal sullenly retreated to the Elbe, where he formed the siege of Magdeburg, which had of its own accord declared against the Emperor, and asked for a Swedish garrison. Meanwhile Gustavus had marched to the Oder, and captured the important fortress of Frankfort, which was garrisoned by the imperialists. From there he designed to move to the relief of Magdeburg, now hard pressed by Tilly and Pappenheim. Every motive of honour and policy impelled him to ensure its safety. But unforeseen obstacles presented themselves. In order to march to Magdeburg, it was necessary to cross the territories of Brandenburg and Saxony, and neither of the electors would for a moment think of permitting an act which might seem to the Emperor a violation of their neutrality. While Magdeburg was in its death throes fruitless negotiations continued. Both the electors remained stubbornly immovable. At last in desperation Gustavus appeared at Berlin with a more potent argument at his back in the shape of an army, and forced the unwilling George William to throw open to him the fortress of Spandau. But it was too late. Saxony had still to be dealt with, and while Saxony was deliberating Magdeburg fell. [Sidenote: =Fall of Magdeburg.=] On May 20th, Pappenheim stormed the town. Amid the confusion of the assault the houses caught fire. The imperialist soldiers, maddened by victory and plunder, lost all self-control, and amid the roar of the flames and the crash of falling houses ensued a scene of carnage, of outrage, and of horror, at which Europe stood aghast. By the next morning the cathedral alone showed gaunt against the sky, amid a mass of blackened ruins, to say where Magdeburg once had been.