The majestic and solemn Cathedral of San Lorenzo was built from the ninth century and was rebuilt until the sixteenth century, which explains the juxtaposition of different architectural styles both outside and inside. In 1118 the church was consecrated by Pope Gelasius II.

The city cathedral presents the visitor with its beautiful Gothic façade Genovese style (XIII century) with a French influence as shown by the arrangement of portals and central rose window. The Romanesque period date back the side panels with the two portals while the dome (designed by Galeazzo Alessi) and the bell tower are of the sixteenth century. The interior is divided into three naves, it contains numerous sculptures and paintings. Along the left aisle is the chapel of St. John the Baptist where the bones of San Lorenzo contains; down the right aisle leads instead to the Museum of the Cathedral Treasury which houses masterpieces of religious art including the Sacred Basin which legend identifies with the Holy Grail, the Ark of the ashes of St. John the Baptist and other objects related to the worship of patron of the city.