The Index Librorum Prohibitorum (English: List of Prohibited Books) was a list of publications deemed heretical, anti-clerical or lascivious, and therefore banned by the Catholic Church.
The 9th Century witnessed the creation of what is considered to be the first index, called the Decretem Glasianum. Much later, a first version (the Pauline Index) was promulgated by Pope Paul IV in 1559 and which lasted less than a year, being then replaced by what was called the Tridentine Index (because it was authorized at the Council of Trent), which relaxed aspects of the Pauline Index that had been criticized and had prevented its acceptance.
The aim of the list was to protect the faith and morals of the faithful by preventing the reading of heretical and immoral books.
“Catholic libraries kept some books off the general stacks and subject to limited distribution. When it came to college students, permission from the local bishop was required before students could read them. The Index was particularly hard on French literature of the Enlightenment and post-enlightenment periods. Bellairs, no friend of censorship, once remarked that a Frenchman would be illiterate in the literature of his own country if he paid attention to the Index. In any event, one of the earliest and most welcome reforms of Vatican II was to throw the whole thing out.”
In mentioning the “cumbersome grilles, cages, steel rooms, and cyclone-fenced enclosures that now take up so much space,” Bellairs was remembering the collection of materials under lock and key at the Notre Dame library, briefly mentioned in his February 27, 1959, Scholastic article. Bowen confirms the library did have such an area, adding it was known by some as the Grid but cannot recall if books on the Index were located there:
“I'm sure that it was, because the University took the Index very seriously. A few members of the Holy Cross order who had responsible positions in the administration had the power, delegated by the Bishop of Fort Wayne, in whose diocese South Bend was located, to grant permission to read these books. I assume that they did so pretty freely for faculty members, but students were a different matter. During my junior year the Liberal and Fine Arts College invited a noted literary critic to give a series of lectures, and he announced that he would talk about four novels: Tolstoy's War and Peace, Dostoyevsky's Brothers Karamazov, Stendhal's The Charterhouse of Parma, and Gide's The Counterfeiters. The college was much embarrassed because the last two were on the index. Students who wanted to read the books in order to attend the lectures had to go to Academic Dean, Father Soleta, and ask permission but he wouldn't give it unless you had already read the two Russian novels. I was among this elite company, so I received permission but I never did get around to reading the books. I wouldn't be surprised if within the grilles and grids, in addition to works officially on the index, the library also used this area to sequester other books that one or another authority figure had decided were not good for students to have access to.”
- Bellairs visits the Notre Dame library to check out a book, only to discover said book "had been placed inside the Grill" ("The lock on this massive dungeon had long ago rusted shut, so the locksmith and janitor went to work.") (Scholastic: "twice the brinded cat hath mewed") .
- Sister M. Fiorello uses Marx's Communist Manifesto in her coursework but isn't sure what to do when the local bishop does not give her Index permission (Saint Fidgeta and Other Parodies, 45).