The current building (1459-62) stands on the ancient Romanesque parish church of Saint Mary (some fragments are kept in the crypt) and is one of the samples that best represents Renaissance architecture, despite some Gothic elements such as the roof with two slopes, the large mullioned windows that flood the room with light and the central oculus. The facade, made of travertine, has four pilasters (pillars slightly overlapping the wall) that frame three areas corresponding to the three naves (first attempt of the fifteenth century to relate the internal and external architecture of a sacred building); On the tympanum you can see the coat of arms with the emblem of the Holy See of Pius II Piccolomini. Continuing inside, we notice that the structure, hidden by the roof with two slopes, is a Latin cross and is divided into three naves of the same height (church hall), separated by pillars with semi-columns leaning against each other. At the end of the entire structure is placed the polygonal apse divided into three chapels.