Classical elements included the Arch of Constantine ( exterior , main façade ) and the great vaulted spaces of the Baths of Diocletian ( interior ) ; prominent siting at the intersection of two of Pierre L'Enfant 's avenues , with an orientation that faced the United States Capitol just five blocks away ; a massive scale , including a façade stretching more than 600 feet and a waiting room ceiling 96 feet above the floor ; stone inscriptions and allegorical sculpture in the Beaux - Arts style ; expensive materials such as marble , gold leaf , and white granite from a previously unused quarry .