This state might partly arise from Luther's want of brotherly feeling; but it had other causes also. Soliman had come to fulfil a promise made to King Ferdinand. The latter having demanded, in 1528, the surrender of Belgrade, the Sultan had haughtily replied, that he would bring the keys himself to Vienna. In fact, the Grand Turk, crossing the frontiers of Germany, had invaded countries "on which the hoofs of the Mussulman war-horses had never trod," and eight days before the conference at Marburg, he had covered with his innumerable tents the plain and the fertile hills in the midst of which rise the walls of Vienna. The struggle had begun under ground, the two parties having dug deep galleries beneath the ramparts. Three different times the Turkish mines were sprung; the walls were thrown down;[297] "the balls flew through the air like a flight of small birds," says a Turkish historian; "and there was a horrible banquet, at which the genii of death joyously drained their glasses."[298] [297] Ipsam urbem in tribus locis, suffoso solo et pulvere supposito disjicit et patefecit.--(L. Epp. iii. p. 518.) [298] Dschelalsade, quoted by Ranke. Luther did not keep in the background. He had already written against the Turks, and now he published a _Battle Sermon_. "Mahomet," said he, "exalts Christ as being without sin; but he denies that he was the true God; therefore he is his enemy. Alas! to this hour the world is such that it seems everywhere to rain disciples of Mahomet. Two men ought to oppose the Turks: the first is Christian, that is to say, Prayer; the second is Charles, that is to say, The sword." And in another place, "I know my dear Germans well, fat and well-fed swine; as soon as the danger is removed, they think only of eating and sleeping. Wretched man! if thou dost not take up arms the Turk will come; he will carry thee away into his Turkey; he will there sell thee like a dog; and thou shalt serve him night and day, under the rod and the cudgel, for a glass of water and a morsel of bread. Think on this; be converted, and implore the Lord not to give thee the Turk for thy schoolmaster."[299] [299] Heer predigt wider die Türken.--(L. Opp. (W.) xx. p. 2691.) [Sidenote: VARIETY OF CHARACTER.] The two arms pointed out by Luther were, in reality, vigorously employed; and Soliman, perceiving at last that he was not the "soul of the universe," as his poets had styled him, but that there was a strength in the world superior to his own, raised the siege of Vienna on the 16th October; and "the shadow of God over the two worlds," as he called himself, "disappeared and vanished in the Bosphorus."