Image: President's Sphere - Monolithic Dome Churches

The Pantheon, built in Rome in A.D. 126, still remains in use today. It is a circular cylinder carrying a half sphere dome with a diameter of 142 feet. It is, perhaps, our first example of an antique monolithic dome. The Romans are credited with being the first to develop poured concrete construction, and were the first to exploit the dome as an architectural feature. The oculus, a circular window at the top of a dome, permits light throughout the entire structure.