Construction of the Pantheon commenced in 27 BC by the statesman Marcus Vipsanius Agrippa. It was a building of the classical style, rectangular with a gabled roof supported by a colonnade on all sides. I t was completely rebuilt by the emperor Hadrian sometime between AD 118 and 128, with some alterations made in the early 3rd century by the emperors Lucius Septimius Severus and Caracalla. It is a circular building of concrete faced with brick, with a great concrete dome rising from the walls and with a front porch of Corinthian columns supporting a gabled roof with a triangular pediment.
             Beneath the porch are huge bronze doors, 24 feet (7m) high, the earliest large examples of this type.
             The Pantheon is remarkable for its size, its construction, and its design. The dome was the largest built until modern times, measuring about 142 feet (43m) in diameter and rising to a height of 71 feet (22m) above its base.
             The Pantheon has been an inspiration for architects and architecture. It is renowned as one of the most celebrated edifices in the world. How right this is can be seen by leafing through the illustrations of any standard history of architecture, noting how domed rotundas with temple-front porches appear. These progeny of the Pantheon are ubiquitous, the result more than anything of all-encompassing imagery expressing universality that made it possible for the building to be meaningful in different ways in different historical periods. It has always been a symbol of Rome, and of things Roman as they have been variously conceived over the centuries. Again and again, it has provided inspiration in response to needs unknown when it was built. Unlike the vast palaces, the imperial fora, and the other stupendous works of the Caesars, it has continued to stand.
             The Pantheon is a truly large interior volume, a building whose size seemed all but incommensurable and could not during much of its long existence have been duplicat...