The dome itself is amazing. At nearly 142 feet, the dome is larger than the domes of the Capitol Building in Washington, D.C., St. Pauls in London, the Pantheon in Rome, and even St. Peters in Vatican City. The dome remained the largest dome in the world until modern materials permitted the construction of stadium-sized domes such as the Metrodome in Minneapolis
The inside of the Duomo contains intricately decorated marble floors, but the rest of the inside is fairly simple for an Italian church, this is perhaps because the fresco adorning the dome is one of the best in Italy. The fresco, designed by Giorgio Vasari and Federico Zucchari is called "The Last Judgement." One side of the dome is painted with images of heaven and the other with images of hell culminated in a very nasty looking devil.