An unusual feature in the Duomo is the "graffiti", precious marble inlay pavement, which was started in 1369 and took nearly 200 years to complete.
Fifty-six individual fields with philosophers, sibyls, virtues, allegories and biblical scenes provide a picture from Classical history to Christianity
and to the founding of the city of Siena. Viewing these graffiti was the highlight of my visit to the Duomo. Unfortunately, about half were covered up.
One must return in August when they are all uncovered.