Of the 12C building, the remarkable Romanesque cupola over the transept crossing still remains. In the chapel adjoining the vestry, note the flamboyant Gothic tomb of Pope John XXII and, at the entrance to the choir stalls, a fine bishop's seat made of white marble, decorated with a lion and an ox, symbolising St Mark and St Luke. The tympanum frescos by Simone Martini can now be seen in the Pope's Palace.