Michelangelo once said that the Pantheon was “Built by angels, not by men.”

The porch to the rotunda, which is under a coffered concrete dome, with a central opening to the sky. Almost two thousand years after it was built, the Pantheon's dome is still the world's largest unreinforced concrete dome. It is one of the best-preserved of all Ancient Roman buildings.

The Pantheon's large circular domed cella was unique in Roman architecture. it became a standard exemplar when classical styles were revived, and has been copied many times by later architects.