The Pantheon is a former Roman temple and, since 609 AD, a Catholic church (Basilica of St. Mary and the Martyrs), on the site of an earlier temple commissioned by Marcus Agrippa during the reign of Augustus.

The building is cylindrical with a portico of large granite Corinthian columns under a pediment. A rectangular vestibule links the porch to the rotunda, which is under a coffered concrete dome, with a central opening (oculus) to the sky. Almost two thousand years after it was built, the Pantheon's dome is still the world's largest unreinforced concrete dome. The height to the oculus and the diameter of the interior circle are the same: 142 feet. It is one of the best-preserved of all Ancient Roman buildings, in large part because it has been in continuous use throughout its history and is visited by over 6 million people a year.