The Roman Index of Forbidden Books (Betten)/Section I/Chapter 4
4. The Roman Index.
More than thirty years after the first index of Henry VIII had appeared, the first Roman Index of Forbidden Books was compiled and issued by Paul IV, 1559, It remained in force only a few years, till 1564, when the so-called Tridentine Index was published under Pius IV. It was called "Tridentine," because it had been drawn up by a commission appointed for this purpose by the Council of Trent. It was milder than the Index of Paul IV, and contained divers "Index rules," the forerunners of the general decrees embodied in the Constitution "Officiorum ac munerum."
The Tridentine Index remained the Roman Index for more than three hundred years. Its "rules" were occasionally modified, new regulations were added or old ones abrogated, other books were inserted in the catalogue; but the essential features remained the same.
In 1897, Leo XIII took the matter up again. The index of forbidden books was thoroughly revised. About a thousand titles were dropped. The "rules," too, were revised, "to make them milder, without altering their nature, so that it cannot be difficult or irksome for any person of good will to obey them."
This, then, represents the whole book legislation of the Church. There are no other documents, except the decrees by which, as occasion demanded, individual books were forbidden. The encyclical of Pius X on Modernism merely enjoins on the bishops special vigilance in regard to publications infected with modernistic views.
This universal legislation, however, does not preclude the local prohibition of books by bishops or other ecclesiastical authorities. Thus Spain had, until 1820, its own Index, controlled by the Spanish Inquisition.