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, or all, and theon, or 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, nor even the phenomenal technical difficulties posed by so massive a construction; rather, it's the remarkable unity of the building. 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."
To do the interior justice defied even Byron. He piles up adjectives, but none seems to fit: "Simple, erect, severe, austere, sublime." Although little is known for sure about the Pantheon's origins or purpose, it's worth noting that the five levels of trapezoidal coffers (sunken panels in the ceiling) represent the course of the five then-known planets and their concentric spheres. Ruling over them is the sun, represented symbolically and literally by the 30-foot-wide eye at the top. The heavenly symmetry is further paralleled by the coffers: 28 to each row, the number of lunar cycles. In the center of each would have shone a small bronze star. Down below the seven large niches were occupied not by saints, but, it's thought, by statues of Mars, Venus, the deified Caesar, and the other "astral deities," including the moon and sun, the "sol invictus." (Academics still argue, however, about which gods were most probably worshipped here.)
One of the reasons the Pantheon is so well preserved is the result of it being consecrated as a church in AD 608. (It's still a working and Mass-holding church today, and it's the church name, the Santa Maria degli Angeli e dei Martiri, that you'll see on official signs.) No building, church or not, though, escaped some degree of plundering through the turbulent centuries of Rome's history after the fall of the empire. In 655, for example, the gilded bronze covering the dome was stripped. Similarly, in the early 17th century, Pope Urban VIII removed the bronze beams of the portico. Most of its interior marble facing has also been stripped and replaced over the centuries. Nonetheless, the Pantheon suffered less than many other ancient structures. The temple's original bronze doors have remained intact, if restored and even melted down and recast at one point, for more than 1,800 years.
The Pantheon is also one of the city's important burial places. Its most famous tomb is that of Raphael (between the second and third chapels on the left as you enter).
Mass takes place on Sunday and religious holidays at 10:30: it's open to the public, but you are expected to arrive before the beginning and stay until the end. General access usually resumes at about 11:30.