The cathedral was built by Bernardo Rossellino where the ancient parish church of Santa Maria used to stand, it faces a different direction to the ancient church, yet it was specifically constructed to fit into this square being commissioned by Pope Pio I
The travertine facade was also designed by Rossellino. Four pilasters divide it into three areas corresponding to the internal layout of one nave and two aisles. The string-course frame divides the facade into two areas; the lower one has three doorways, the upper one has three large arches supported by columns. Beneath the side arches classicized niches were created, the central one contains the roundel.
The facade’s gable is dominated by the Piccolomini coat of arms surrounded by friut festoons.
The external walls of the church and apse both have gothic windows, allowing a great deal of light to enter, creating a magical atmosphere inside.
The tall belltower was seriously damaged with the 1545 earthquake and subsequently repaired in 1570.
The interior is still structurally Gothic in style, it has a latin cross shape divided into one nave and two aisles, all of the same height. The middle nave is slightly larger than the side aisles. Two rows of pilasters with semi-columns and raised decorated capitals, divide the aisles.
The apse is divided into three chapels, the main one has the choir. Another two chapels are shaped because of the land on which the apse has been built. The church has many paintings of the most famous artists of the period commissioned by Pope Pio II.
by the cross vaulting arms, each of which has a large window. All this area has yielded