Built in the 11 and 13C, supposedly on the site of a collegiate church founded by Charlemagne, this imposing cathedral was the cure of Zwingli who preached there from 1519 until he died. Framing the façade are two high towers topped with wooden cupolas covered with sheets of metal. The south tower is decorated with a huge statue of Charlemagne (the original is in the crypt). The modern stained-glass windows are by Giacometti (1932).