Santa Maria Assunta (Our Lady of the Assumption - Cathedral). This is an essentially Romanesque structure with a central nave and two aisles and transept. It was built in the second half of the twelfth century after the city had been devastated by Fredrick Barbarossa. An earlier tenth-century cathedral had stood on the same site dedicated to Saint Primiano. The current portico in front and the bell tower are respectively fifteenth and sixteenth century.

The lowest section holds a refined portal with sculptured architrave and jambstones. There are two pulpits to the sides of the portico,

The two sections above are subdivided into three vertical sections with rose windows and ogival arches

The central arch of the top horizontal section holds a large mosaic by Solsterno with a benedictory Christ. The part of the bell tower contemporary to the cathedral is made of Roman and early mediaeval fragments found elsewhere.

Theinside, of the Cathedral was profoundly redecorated in the seventeenth and eighteenth centuries (see the four altars in the left aisle by Valadier). It still preserves, however, its original layout, the "Cosmatesque" flooring in the nave (also still visible in the portico outside) and the apse.

The apse was marvellously frescoed between 1467 and 1469 with scenes of the life of Virgin Mary by Filippo Lippi (who lies buried on the right side of the transept) together with his helpers fra' Diamante and Pier Matteo d'Amelia.

Other noteworthy features: a precious altar cross on parchment applied to wooden board, painted by Alberto Sotio in 1185.

The frescoes by Pinturicchio (Bernardino di Betto), in the Chapel of Bishop Eroli and other sixteenth century personages in the chapel next to it;

a fourteenth century wooden polychromatic statue depicting Our Lady with Child and the sixteenth century choir with altar, tabernacle and painted stalls, in the Chapel of the Relics.