but it was necessary to proceed cautiously, and he assured Pope Adrian VI that he was anxious to reform the order and punish the knights who had adopted Lutheran doctrines. Luther for his part did not stop at the suggestion, but in order to facilitate the change made special efforts to spread his teaching among the Prussians, while Albert's brother, Margrave George of Brandenburg-Ansbach, laid the scheme before their uncle, Sigismund I the Old of Poland. Duke in Prussia After some delay Sigismund assented to the offer, with the provision that Prussia should be treated as a Polish fiefdom; and after this arrangement had been confirmed by a treaty concluded at Kraków, Albert pledged a personal oath to Sigismund I and was invested with the duchy for himself and his heirs on 10 February 1525. The Estates of the land then met at Königsberg and took the oath of allegiance to the new duke, who used his full powers to promote the doctrines of Luther. This transition did not, however, take place without protest. Summoned before the imperial court of justice, Albert refused to appear and was proscribed, while the order elected a new Grand Master, Walter von Cronberg, who received Prussia as a fief at the imperial Diet of Augsburg. As the German princes were experiencing the tumult of the Reformation, the German Peasants' War, and the wars against the Ottoman Turks, they did not enforce the ban on the duke, and agitation against him soon died away. In imperial politics Albert was fairly active. Joining the League of Torgau in 1526, he acted in unison with the Protestants, and was among the princes who banded and plotted together to overthrow Charles V after the issue of the Augsburg Interim in May 1548. For various reasons, however, poverty and personal inclination among others, he did not take a prominent part in the military operations of this period. The early years of Albert's rule in Prussia were fairly prosperous. Although he had some trouble with the peasantry, the lands and treasures of the church enabled him to propitiate the nobles and for a time to provide for the expenses of the court. He did something for the furtherance of learning by establishing schools in every town and by freeing serfs who adopted a scholastic life. In 1544, in spite of some opposition, he founded Königsberg University, where he appointed his