One of the great Lombard Romanesque churches, built from 1137 on the site of an earlier church dating to 774 AD. The facade is covered in red, white and black marble; the roof in stone ardesia shingles like the mountain villages above the city.
Inside: Lorenzo Lotto frescoes, extraordinary inlaid wood panels at the altar (ask the custodian to lift the covers), carved confessionals by Andrea Fantoni, and a famous organ. Don't miss the medieval iron measuring bars embedded in the outer wall — used in the open market days before standard units existed.