The interior of the drum contains sixteen fluted Corinthian pilasters, worked in plaster, surmounted by a sophisticated broken entablature. This ornamentation gives a hint of what the decoration in the nave would have looked like had the original decorative scheme been carried out. The gallery around the drum is accessible from an outside door, and there are eight rounded windows of clear glass. The interior face of the dome, originally intended to be clad in a rich mosaic, is in exposed concrete. The dome reaches a height of over 100 feet and has a diameter of 37 feet.