Basilica di San Petronio

The Basilica di San Petronio presides over Bologna's Piazza Maggiore with a famously unfinished facade — half clad in marble, half bare brick — and is the largest brick church in the world by enclosed volume at roughly 258,000 m³. Construction began in 1390 under Antonio di Vincenzo, and the building breaks from medieval convention with a north-south axis rather than the standard east-west orientation, placing the high altar at the southern end. The original plan would have surpassed St. Peter's Basilica in Rome; legend holds that the papacy intervened to prevent the civic church from outgrowing the Vatican. Inside, Giovanni Cassini laid one of Europe's longest meridian sundials into the marble floor in 1655, using a hole in the vaulting to project sunlight across the nave — a precision astronomical instrument still visible today. The basilica is open daily and fully wheelchair-accessible.