Work on this basilica started in 1390 but was only completed in the 17C when the vaults were finally built! The façade is remarkable for its central doorway, a major work by Siena-born sculptor Jacopo della Quercia. The vast interior is home to a plethora of works of art, of which the frescoes by Giovanni da Modena are of particular interest. If you raise your eyes, you will see an oculus in the vaulting through which the midday sun hits a meridian line traced on the floor.