The church is essentially an example of Romanesque architecture, with a nave and two side-aisles crossed by a transept, although subsequently modified.

It was built from the second half of the twelfth century after the city had been devastated by Frederick Barbarossa's troops, over an area where there had previously stood an earlier cathedral, dedicated to Saint Primianus (San Primiano)[1] and destroyed by the emperor.

The most striking feature of the upper façade is the Byzantine-hieratic mosaic portraying Christ giving a Benediction, signed by one Solsternus (1207).

Another survival is the frescoed apse with four scenes from the Life of the Virgin, begun in 1467 by Filippo Lippi and completed two years later by his pupils Fra' Diamante and Piermatteo Lauro de' Manfredi da Amelia.

Also noteworthy are the altar cross by Alberto Sozio, dated 1187, a Byzantine icon donated to the city by Barbarossa as a sign of peace and the frescoes by Pinturicchio in the Chapel of the Bishop of Eroli.