The favourable relations between the Church and the printers were checked by the Humanistic movement, which, a generation or more before the Reformation, began to bring into question the authority of the Church and the infallibility of the Papacy. The influence of the Humanistic teachers was so largely furthered by the co-operation of the printers that the jealousy and dread of the ecclesiastical authorities were promptly aroused, and they began to utter fulminations against the wicked and ignorant men who were using the art of printing for misleading the community and for the circulation of error. Ecclesiastics who had at first favoured the widest possible circulation of the Scriptures, now contended that much of the spread of heresy was due to the misunderstanding of the Scriptures on the part of readers who were acting without the guidance of their spiritual advisers. The Church now took the ground that the reading of the Scriptures by individuals was not to be permitted and that the Bible was to be given to the community only through the interpretations of the Church. At the same time, the authority of the Church was exerted to repress or at least to restrict the operations of the printing-press and to bring printers and publishers under a close ecclesiastical supervision and censorship. It was, however, already too late to stand between the printing-press and the people. Large portions of the community had become accustomed to a general circulation of books and to the use without restriction of such reading matter as might be brought within their reach, and this privilege they were no longer willing to forego. In Spain, in Italy, and in France, the censorship of the Church soon became sufficiently burdensome to hamper and to interfere with publishing undertakings and to check the natural development of literary production. Even in Italy, however, the critical spirit was found to be too strong to be crushed out, and from Venice, which became the most important of the Italian publishing centres (because it was the freest from papal control) it proved possible to secure for the productions of the printing-press a circulation that was practically independent of the censorship of Rome. The importance of Frankfort as a centre of the trade in books began with the first years of the 15th century, when the dealers in manuscripts were present with booths at the Frankfort Fair. The manuscript dealers came together once a year also at the fairs of Salzburg, Ulm, and Nordlingen, but the book-trade at Frankfort soon assumed a pre-eminence that it did not lose for two centuries. The earliest date at which is chronicled the sale at the Frankfort Fair of printed books was 1480. For these earlier sales of manuscripts and printed books, there was apparently no censorship or official supervision.