Siena Cathedral (Duomo di Siena) was constructed between 1215-1263. It is unique because of the layers of white and green marble. It is beautiful. The front was being repaired so I could not get a picture of it. The cathedral would have been much larger; but, the wing to be constructed was not because of the plague of 1348. You are not allowed to take pictures of the inside of the cathedral, but I got a few.