The Pantheon in Rome

The Ancient Romans were skilled at concrete construction. When they built the Pantheon in Rome, they applied these skills to the Greek classical orders. They gave their Pantheon massive 25-foot thick walls to support a huge dome made of solid concrete. With a diameter that measures 43.4 meters, the dome of the Roman Pantheon ranks as the world's largest dome made of unreinforced solid concrete.

The ceiling of the Pantheon dome has symmetrical rows of coffers (sunken panels) and a round oculus (opening) at the center. Sunlight streaming through the oculus illuminates the Pantheon rotunda.