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. It's thought that the majestic circular building was actually designed by Hadrian, as were many of the temples, palaces, and lakes of his enormous villa at Tivoli. Hadrian nonetheless retained the inscription over the entrance from the original building (today, unfortunately, replaced with modern letters) that named Agrippa as the builder. This caused enormous confusion among historians until, in 1892, a French architect discovered that all the bricks used in the Pantheon dated from Hadrian's time.
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."
To do the interior justice defied even Byron. He piles up adjectives, but none seems to fit: "Simple, erect, severe, austere, sublime." Not surprising, perhaps, when describing a dome 141 feet high and the same across. Although little is known for sure about the Pantheon's origins or purpose, it's worth noting that the five levels of trapezoidal coffers represent the course of the five then-known planets and their concentric spheres. Then, ruling over them, comes the sun represented symbolically and literally by the 30-foot-wide eye at the top. The heavenly symmetry is further paralleled by the coffers themselves: 28 to each row, the number of lunar cycles. Note how each coffer takes five planetary steps toward the wall. Then 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. We may never know for sure.)
The Pantheon is by far the best preserved of the major monuments of imperial Rome, a condition that 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 Basilica of Saint Mary and the Martyrs, that you'll see on the official signs.) No building, church or not, 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. Although the legend holds that the metal went to the baldacchino (canopy) over the high altar at St. Peter's Basilica, the reality may be worse—it went to cannons at Castel Sant'Angelo. 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.
Today, the Pantheon serves as 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). The inscription reads "Here lies Raphael; while he lived, mother Nature feared to be outdone; and when he died, she feared to die with him." Two of Italy's 19th-century kings are buried here, too: Vittorio Emanuele II and Umberto I. The tomb of the former was partly made from bronze that had been taken from the Pantheon by Urban VIII to cast as cannon. Thankfully, 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. Be sure to ponder them as you leave.
One-hour tours (€10) are run regularly in English; check at the information desk on your right as you enter.