In 1530, there came to Vienna a group of Jesuits who did much to strengthen the machinery of censorship. The undertakings of the printers and of the booksellers decreased in direct proportion with the growth of the influence of the Jesuit advisers of the emperor. In 1523, the production and sale throughout the empire of the German Bible is prohibited. In 1564, the Elector of Bavaria orders that the work of the publishers must be restricted to printers whose Catholic orthodoxy has been duly tested. In this year, the Elector begins the issue of an annual list of books that were to be permitted. In 1569, the use in the schools of Bavaria of certain Latin classics, including the works of Virgil, Horace, and Ovid, was prohibited. In 1616, the Elector appointed Catholic commissioners of censorship for each town in Bavaria. The University of Ingolstadt became the centre of the work of the Jesuits, who, in Bavaria as in Vienna, had secured the direction of censorship. In 1579, under Rudolf II, the Jesuits were called upon to put into shape a more effective censorship for the empire. Under the régime thus established, the standard of thought for the political action and for the religious belief of Germany was to be fixed in Rome and in Madrid. Under the direction of the Jesuit censors in the year 1579, no less than twelve thousand books in German and two thousand in Bohemian were burned by the public hangman in the town of Gratz.[59] In the same year, an imperial commission was appointed, with headquarters at Frankfort, which was charged with the supervision of the book production of the empire. The operations of this commission were very largely controlled by the interests, real or imaginary, of the Catholic Church, and the personal supervision and arbitrary censorship of the ecclesiastics, had not a little to do with the disintegrating of publishing undertakings in Frankfort and with the transfer, some years later, to Leipsic of the leadership in the business of book production and book distribution.