When such powerful princes became interested, Leo was startled. He summoned Luther to Rome, to be tried by Prierias. Luther, not daring to refuse, and not willing to obey, wrote to his friend Spalatin to use his influence with the elector to have his cause tried in Germany; and the pope, willing to please Frederic, appointed De Vio, his legate, to investigate the matter. Luther accordingly set out for Augsburg, in obedience to the summons of De Vio, although dissuaded by many of his friends. He had several interviews with the legate, by whom he was treated with courtesy and urbanity, and by whom he was dissuaded from his present courses. But all the persuasion and argument of the cardinal legate were without effect on the mind of Luther, whose convictions were not to be put aside by either kindness or craft. De Vio had hoped that he could induce Luther to retract; but, when he found him fixed in his resolutions, he changed his tone, and resorted to threats. Luther then made up his mind to leave Augsburg; and, appealing to the decision of the sovereign pontiff, whose authority he had not yet openly defied, he fled from the city, and returned to Wittemberg, being countenanced by the elector, to whom he also addressed letters. His life was safe so long as Frederic protected him. [Sidenote: The Leipsic Disputation.] The next event in the progress of Luther was the Leipsic disputation, June, 1519. The pope seemed willing to make one more effort to convince Luther, before he proceeded to more violent courses. There was then at his court a noble Saxon, Charles Miltitz, whose talents and insinuating address secured him the high office of chamberlain to the pope. He accordingly was sent into his native country, with the dignity of legate, to remove the difficulties which De Vio had attempted. He tried persuasion and flattery, and treated the reformer with great civility. But Luther still persisted in refusing to retract, and the matter was referred to the elector archbishop of Treves. While the controversy was pending, Dr. Eck, of the university of Ingolstadt, a man of great scholastic ingenuity and attainment, and proud of the prizes of eight universities, challenged the professors of Wittemberg to a public controversy on Grace and Free Will. He regarded a disputation with the eye of a practised fencer, and sought the means of extending his fame over North Germany. Leipsic was the appointed arena, and thither resorted the noble and the learned of Saxony. Eck was among the first who arrived, and, soon after, came Carlstadt, Luther, and Melancthon. [Sidenote: Principles of the Leipsic Disputation.]