I want to know the answer to the following question:
Which Italian cathedral displays polychrome marble and mosaic on the gable?
All the background I'm provided with is that "The gable is usually richly decorated with arcading or sculpture or, in the case of Italy, may be decorated with the rest of the façade, with polychrome marble and mosaic, as at Orvieto Cathedral.". Is that enough to answer the question?
Answer: yes