The noble Piccolomini family, one of the most prestigious in Siena, had among its illustrious members two figures of major importance who played a leading role in the history of the art in the cathedral: Pope Pius II (1458-1464), born Enea Silvio Piccolomini, a humanist and art patron, and his nephew Francesco Todeschini Piccolimini, also elected pope in 1503, taking the name of Pius III, but dying less than a month later. It was he who commissioned, as Cardinal Archbishop of Siena, two of the most important art works created inside the cathedral in the early Renaissance: the erection of the marble altar in the fourth bay of the left aisle and the decoration of the room opening off the same aisle known as the Piccolomini Library, devoted to the glorification of the memory of his uncle Pius II.