Basilica di San Petronio

One of Europe's largest brick churches, deliberately stunted by the Pope

The Basilica of San Petronio dominates Piazza Maggiore from its southern side. Begun in 1390, it was the city's gesture of civic pride — built and paid for by the commune rather than the Church, which is why the facade remains half-finished: when papal money paid for the project, work proceeded; when it didn't, work stopped.

Inside, the central nave runs 132 metres long under cross-vaulted ceilings 45 metres high. The most extraordinary feature is the meridian line set into the floor in 1655 by Gian Domenico Cassini, a 67-metre brass strip that the sun crosses through a small hole in the roof. Cassini used it to measure the length of the solar year and prove the irregularity of Earth's orbit — practical astronomy done inside a church.

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The original plan for San Petronio called for a building larger than St Peter's in Rome. Pope Pius IV blocked it by diverting funding to the Archiginnasio next door, which physically prevented eastward expansion. The marble facade was started in 1538 and never finished — you can still see the line where the work simply stopped.