The Basilica di San Petronio is the 5th largest church in the world. As you can see the top half was never finished. This makes it a rather unique church today.
In this picture, you can see the sculptures by Jacopo della Quercia on the top of the main doorway, the Porta Magna.
The next three pictures are of the Palazzo Communale, also found in Piazza Maggiore.
Right next to Piazza Maggiore, is Piazza del Nettuno. This piazza is slightly smaller and opens up into Piazza Maggiore. Here you will find the interesting statue of Neptune.
The following two pictures were also taken while in Piazza del Nettuno. I took the first picture earlier when all the scaffolding and workmen had the basilica roped off. The second picture is of the Palazzo di Re Enzo (Palace of King Enzo).