The stone frame of the arch is sculpted with delicate spirals of fronds with either flowers, animals, or faces in the center.
The nave is subdivided into three aisles, of which the central one is the widest and tallest, separated by two arcades of round arches supported by Corinthian columns.
On the counterfaçade is a large fresco depicting the Last Judgment (1596) painted by Ferraù Fenzoni known as "Il Faenzone".
Many episodes and figures, including that of the seated Christ, though more condensed in this space, they are derived from Michelangelo's fresco at the Sistine Chapel.
In the crypt are three sculptures previously on the west front, attributed to Giovanni Pisano and to "Il Rubeus".