In 1492, the Archbishop of Siena, Cardinal Francesco Nanni Todeschini-Piccolomini (later Pope Pius III), founded the Piccolomini Library (Libreria Piccolomini) in the cathedral to store the most valuable family books and manuscripts with colorful miniatures from the collection of his uncle Enea Silvio Bartolomeo Piccolomini (Pope Pius II).
The fresco "The Coronation of Pope Pius III", created by Pinturicchio in 1504 on commission from the heirs of the pontiff, who died on October 18, 1503, is located above the entrance to the Piccolomini Library.