The Congregation of the Index was set up in 1571 by Pope Paul V, as part of the policy of control and repression he pursued during his papacy. The aim was to identify among books already printed, including ancient works, those to be prohibited on account of their opposition to the Catholic faith on grounds of heterodoxy and obscenity (such as the Decameron, subjected to thorough revision in the 1570s, by Salviati and others). At the same time, preventive censorship was applied to all new texts, consenting to publication only after formal approval by the local Congregation, thereby carefully filtering what could be printed and read. In 1559 an Index of Prohibited Books had been compiled and published at the instigation of Paul IV Carafa, though its extreme severity was more relaxed in the so-called Tridentine Index published in 1564. Following the creation of the Congregation, new Indices were published in 1590, 1593 and 1596 (this last named the Clementine Index, after Clement VIII). Although recent studies have revealed difficulties and inaccuracies in the workings of the Congregation, it had a powerful impact, especially from the 1570s on, as testified by the official requests for permission to read prohibited texts, as in Tasso’s letters, and by the silence surrounding authors such as Aretino and Machiavelli, whose works were prohibited in 1559.

Title page of the Index of Forbidden Books, Venice 1564