The Pantheon ("[temple] of all the gods") is a former Roman temple, now a church, in Rome, Italy. It was built on the site of an earlier temple commissioned by Marcus Agrippa during the reign of Augustus (27 BC – 14 AD). It was completed by the emperor Hadrian and probably dedicated about 126 AD. Its date of construction is uncertain, because Hadrian chose not to inscribe the new temple but rather to retain the inscription of Agrippa's older temple, which had burned down.
The building is circular 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 (43 m).
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 since the 7th century, the Pantheon has been used as a church.
The Pantheon's large circular domed cella, with a conventional temple portico front, was unique in Roman architecture. Nevertheless, it became a standard exemplar when classical styles were revived, and has been copied many times by later architects.