Pope Benedict XIII ordered the reconstruction of this building after the original Romanesque church collapsed, in 1404.
The exterior has lots of finely carved arches, gargolyes and features such as the infamous 'ball rats' that you can spot as you wander around.
The main building that you can see today took around 115 years to complete, with successive architects adding on Gothic vaults, ribs, and high stained glass windows.
Inside you'll find painted panels and ironwork, fine altar pieces, marble sculptures and holy relics.
