Sixtus IV.

laid a basis for the Index by prohibiting the publication of any books which had not previously been licensed by ecclesiastical authority.

Alexander VI.

by a brief of 15O1 confirmed this measure, and placed books under the censorship of the episcopacy and the Inquisition.

Finally, the Lateran Council, in its tenth session, held under the auspices of Leo X., gave solemn ecumenical sanction to these regulations.
The censorship having been thus established, the next step was to form a list of books prohibited by the Inquisitors appointed for that purpose.
The Sorbonne in Paris drew one up for their own use, and even presented a petition to Francis I.that publication through the press should be forbidden altogether.[112] A royal edict to this effect was actually promulgated in 1535.