San Petronio, Bologna

San Petronio is the principal basilica that fronts Piazza Maggiore in Bologna and is dedicated to the city’s patron saint. Construction began in 1390; the building is notable for its very large brick nave and its unfinished façade.

The interior houses numerous chapels, altarpieces and fresco cycles by local and regional artists spanning the 15th to 17th centuries. A prominent scientific feature is a large meridian line cut into the floor and wall for solar observations dated to the 17th century.

The church was planned as a major civic basilica and expanded over the late medieval and Renaissance periods, but the façade and some planned elements were never completed, leaving a contrast between interior richness and exterior incompletion. The basilica has served religious, civic and ceremonial functions in Bologna for centuries.

San Petronio occupies the central position on Piazza Maggiore in Bologna’s historic core, adjacent to other civic monuments and within easy walking distance of the city’s major museums and towers.

• Construction date and size: Construction began in 1390 and the building remained unfinished; the nave length is about 132 metres, making it unusually large for a civic parish church.
• Astronomical meridian: Contains a 17th-century meridian line on the floor used historically for astronomical observations and calendar reckoning inside the church.

What to See #

• Nave and overall dimensions: The long single nave church extends roughly 132 metres in length and is one of the largest brick-built churches in the world.
• Façade and chapels: The unfinished marble façade contrasts with richly decorated interior chapels and altarpieces dating from the 15th to the 17th centuries.
• Cassini meridian line: A large meridian line installed on the floor in the 17th century serves as an astronomical instrument and is one of the basilica's notable scientific features.