A Pope in the Index: Pius II Piccolomini

From the Florence Index of prohibited books published in 1552 up to the 'universal' index which appeared in 1559, the work on the Council of Basel written by Enea Silvio Piccolomini, the future Pius II, in 1440 was always included on account of its conciliarism. It was only during the Council of Trent, in 1563, that the discovery was made that Pius II himself had rejected his earlier opinions in a Bulla retractionis of 1463, which had also been printed. Thus in the Universal Index published in 1564, after the Council of Trent, in which the 1440 work was again included among the prohibited books, it was noted that its author had already condemned the work.