he demanded an explanation, puzzled him as to the meaning of Pack's overtures. A private letter sent by Luther to Link, in which he spoke of George as a fool, and said he mistrusted his promises, led afterwards, on George's learning its contents, to a new and bitter quarrel between the two. The Duke made a violent attack on Luther in a pamphlet, which appeared early in 1521, to which the latter replied with equal violence, denouncing the abuse of 'secret (_i.e._ private) and stolen letters.' George retorted in the same strain, and persuaded his cousin John, to whom he addressed a formal complaint, to prohibit Luther from printing anything more against him without Electoral permission;--a step which effectually silenced his opponent. On November 30, 1528, the Emperor summoned a Diet to meet at Spires on February 21 of the following year, in order that decisive and energetic measures should be taken--as recommended once more by the Pope--to secure the unity and sole supremacy of the Catholic Church. The chief subjects named for deliberation were, the armament against the Turks, and the innovations in matters of religion. As regards the war against the Turks, Luther, who had previously let fall some occasional remarks about certain wholesome effects it would have in checking the designs of the Papacy, let his voice be heard, notwithstanding, in summoning the whole nation to do battle against the fearful and horrible enemy, whom they had hitherto suffered so shamefully to oppress them. Since the latter part of the summer of 1528 he had been engaged upon a pamphlet 'On the War against the Turks,' the publication of which was accidentally delayed till March, when he was busy with his Catechism.