At an early date in the period of the Reformation, Magdeburg, in which the printing business had already secured an assured foothold, had taken an important place among the centres of distribution of Protestant literature. The work of the printers was interrupted for a time in 1518 by the repressive measures of the Catholic Albert of Brandenburg, but after 1528, the presses were again left practically free from civil authority, while the ecclesiastical influence in the city was never important. The book-trade was crushed out for the time by the destruction of the city by Tilly in 1631. [Sidenote: Münster] The city of Münster was another centre for Protestant publications. The excesses of the Anabaptists, who, under John of Leyden and his associates, had possession of the town for a number of months in 1535–36, were, however, well-nigh destructive to its Protestantism and proved fatal to its publishing business. In 1562, an edict issued by the bishop ordered the destruction of all Protestant books in Westphalia and made it a misdemeanour to print, sell, or possess any such books. [Sidenote: Basel] The city of Basel secured at an early date an important position among the centres of publishing. The university, founded in 1460, brought to the city men devoted to scholarly pursuits many of whom took an early interest in the work of the printing press and were ready to give coöperation to the publishers. In 1501, Basel broke away from the imperial control. At that time, there were in the city no less than twenty-six important publishing and printing concerns. During the most active period of its publishing interests, Basel had the advantage over the majority of the German towns in its comparative freedom from censorship either ecclesiastical or civil. The authority of Rome was permitted to exert practically no restrictions upon the productions of the printing-presses; while as a free imperial city, it had the right to claim exemption from any authority other than that of the emperor, whose examiners were too far distant to be able to bring their influence to bear, to any extent, upon the operations of the Basel publishers. It was this freedom that constituted the most important cause of the great development of the book-trade of the city during the 15th and 16th centuries. The leader among the great publishers of Basel, who ranked at the time with Aldus as one of the great publishers of the world, was Johann Froben, the publisher, friend, and close associate of Erasmus. It is the imprint of Froben that is associated with the most important of the volumes of Erasmus, including not only those that secured the approval of Leo X and of other of the Church authorities, but the group which brought the author into sharp criticism with the ecclesiastical censors. During the years between 1460 and 1500, the popes themselves sent to Basel for printing certain books which required more trustworthy work than could be secured in Rome.[145]