Sixtus is the first Pope who undertook to retain for the exclusive action of the Holy Chair, or of the Congregation working under papal instructions, the authority for the production of Indexes, for the prohibition of individual books, for the expurgation of books which in a modified form it was considered important to preserve, and the general supervision of the reading of the Church. Preceding popes had accepted, if not without question at least without formal protest, the claims made by the Inquisition or by the Crown of Spain, by the Inquisition or by the universities of the Low Countries, by the Inquisition of Portugal, and by the University of Paris, to produce Indexes both prohibitory and expurgatory, to publish regulations controlling the production and the use of books, and to institute and to execute punishments for the breach of such regulations. The injunctions of Sixtus, promptly recalled by his successor, seem to have had practically no influence towards the prevention or the lessening of such undertakings on the part of national or local authorities. The successors of Sixtus wisely abandoned the attempt to retain for the Holy Chair the exclusive control of this troublesome business. Sixtus finds place among the authors of Class I for two hundred names, practically doubling the list contained in the Tridentine Index. He utilised, in making his additions, the catalogues of Quiroga, the lexicon of Frisius, and the book-catalogue of the Frankfort Fair as printed in the years 1583–87. The general copying of the names from Frisius and from the Fair catalogues, has the result of bringing into the Sistine lists a number of unimportant writers whose names would otherwise hardly have been preserved, certain others whose books were announced but never came into publication, and, finally, some good Catholic authors, editions of whose writings happened to be brought into print by Frankfort publishers whose imprints had previously been associated with heresy. Among the orthodox ecclesiastics who thus secured undeserved condemnation were Caspar Macer, Bishop of Regensberg, and Andreas Critius, Archbishop of Poland.