The Duomo or Cathedral of Lodi is a building with a Romanesque plan, one of the largest in Lombardy, begun in 1160, completed in the 16th century and fully restored from 1958 to 1965.

The features on the façade worthy of mention: the 12th century porch with column-bearing lions and sculptures on the portal, the large rose window and two Renaissance windows, along with the mighty bell.

The interior has three naves with a raised presbytery and crypt. In the right nave: two altarpieces by Martino and Callisto Piazza, paintings and frescoes from various periods; in the left nave: a plaque adorned with a baroque bust of Cardinal Vidoni, the former bishop of Lodi , fragments of medieval votive frescoes ; in the centre nave: a gilded copper statue of St. Bassianus (13th century), a Gothic sarcophagus altar with ambo and pulpit of Monfrini (1987); behind the altar, late-medieval votive frescoes and a rare Romanesque sculpture depicting the Last Supper. In the high chancel, which is accessed by two staircases, be sure to note the Baroque high altar and the Renaissance choir with intarsia work by Fra ' Giovanni of Verona.

A mosaic by Aligi Sassu (1964) can be seen in the basin of the apse. From the presbytery to the right, by climbing a spectacular grand staircase, you arrive at the Diocesan Museum of Sacred Art - arranged in beautiful 18th century rooms - which contain paintings, statues, sacred furnishings and votive offerings of various ages from various churches in the Lodi area. Return to the Cathedral and descend into the crypt: at the centre be sure to note the urn with the relics of the patron Bassianus and the wooden group of the Pietà (15th cent.) on the left.