One of the wonders of the ancient world, this onetime pagan temple, a marvel of architectural harmony and proportion, is the best-preserved ancient building in Rome. It was entirely rebuilt by the emperor Hadrian around AD 120 on the site of an earlier pantheon (from the Greek pan, all, and theon, gods) erected in 27 BC by Augustus’s general Agrippa.
The most striking thing about the Pantheon is not its size, immense though it is (until 1960 the dome was the largest ever built), nor even the phenomenal technical difficulties posed by so vast a construction; rather, it’s the remarkable unity of the building. You don’t have to look far to find the reason for this harmony: the diameter described by the dome is exactly equal to its height. It’s the use of such simple mathematical balance that gives classical architecture its characteristic sense of proportion and its nobility and why some call it the world’s only architecturally perfect building. The great opening at the apex of the dome, the oculus, is nearly 30 feet in diameter and was the temple’s only source of light. It was intended to symbolize the “all-seeing eye of heaven.”
The Pantheon is by far the best preserved of the major monuments of imperial Rome. Turned into a church in the 7th century, it holds the remains of many luminaries. Its most famous tomb is that of Raphael (between the second and third chapels on the left as you enter). One-hour tours (€10) are run regularly in English; check at the information desk on your right as you enter.