The Basilica of San Petronio is the main church of Bologna, Emilia Romagna, northern Italy. It dominates Piazza Maggiore. It is the tenth-largest church in the world by volume, 132 metres long and 66 metres wide, while the vault reaches 45 metres inside and 51 metres in the facade. With its volume of 258,000 m³, it is the largest (Gothic or otherwise) church built of bricks of the world.
The basilica is dedicated to the patron saint of the city, Saint Petronius, who was the bishop of Bologna in the fifth century. The construction was a communal project of Bologna, not of the bishops: the property was a symbol of communal power that was not transferred from the city to the diocese until 1929; the basilica was finally consecrated in 1954. It has been the seat of the relics of Bologna's patron saint only since 2000; until then they were preserved in the Santo Stefano church of Bologna.