Begun in 1482, the chapel was ordered built by the Operaio del Duomo (head of the cathedral administration) Alberto Aringhieri to house the cathedral’s most illustrious relic, donated in 1464 by Pope Pius II, born Piccolomini, in a beautiful silver reliquary: the right arm of Saint John the Baptist, who baptized Jesus in the waters of the Jordan River. The furnishings and decoration of the . . .