He had arrived, by the end of April, before Frankfurt-on-the Oder, which he took; and he was preparing to succor Magdeburg, which had early pronounced for him, and which Tilly, the emperor's general, kept besieged.

The Elector of Saxony hesitated to take sides; he refused Gustavus Adolphus a passage over the bridge of Dessau, on the Elbe.

On the 20th of May Magdeburg fell, and Tilly gave over the place to the soldiery; thirty thousand persons were massacred, and the houses committed to the flames.

"Nothing like it has been seen since the taking of Troy and of Jerusalem," said Tilly in his savage joy.

The Protestant princes, who had just been reconstituting the Evangelical Union, in the diet they had held in February at Leipzig, revolted openly, ordering levies of soldiers to protect their territories; the Catholic League, renouncing neutrality, flew to arms on their side; the question became nothing less than that of restoring to the Protestants all that had been granted them by the peace of Passau.