A great deal of mystery surrounds the Pantheon; its age, even its name is open to doubt. Most scholars think it was built circa 118 to 128 CE. Whatever the case may be, it remains the most perfectly preserved temple from classical antiquity.
Almost two thousand years later, the Pantheon's concrete dome is still the largest of its kind in the world. Its internal diameter is 43.3 m (142 ft), which is exactly the same as the height from the pavement to the oculus.
The dome, which sits on a six-metre-thick wall, is made up of five rings, each of 28 coffers that diminish in size as it rises. The thickness of the dome also decreases as it rises; at its height it is roughly two metres thick.
The temple was originally built by Marcus Vipsanius Agrippa (63-12 BCE), general, close friend and son-in-law of the emperor Augustus (r. 27 BCE-14 CE). It was completed in either 27 or 25 BCE. A century or so later, in 80 CE, it was damaged by fire and restored by the emperor Domitian (r. 81-96). It was struck by lightning and burned again in 110 before being rebuilt (partially or entirely) in its present form during the reign of the emperor Hadrian (r. 117-138).
Completed around 125-128, the new temple sported an inscription to Marcus Agrippa. The inscription reads: M · AGRIPPA · L · F · COS · TERTIVM · FECIT (Marcus Agrippa, son of Lucius, built this in his third consulship). At some point the original gilded bronze letters disappeared, but the empty matrices of the inscription made it possible to work out what had once been written. In 1894 the hollows were filled with new letters.
There is a second, and much smaller, inscription: IMP · CAES · L · SEPTIMIVS · SEVERVS · ET · IMP · M · AVRELIVS · ANTONINVS · PANTHEVM · VETVSTATE · CORRVPTVM · CUM · OMNI · CVLTV · RESTITVERVNT. (Emperor Septimius Severus and Emperor Aurelius Antoninus restored the worn-out Pantheon to elegance). The great bronze doors of the Pantheon are thought to be the oldest in Rome.
In 609 the Pantheon was converted into a church, that of Sancta Maria ad Martyres, also known as Santa Maria Rotonda. In time, a small bell tower was added to the apex of the pediment. In the 17th century, Pope Urban VIII (r. 1623-44) had this replaced by twin bell towers (often mistakenly attributed to Bernini), which were nicknamed the 'orecchie d'asino' (ears of an ass). The bell towers were removed in 1883.
The Pantheon is the final resting-place of the Renaissance artist Raphael (1473-1520), the Baroque composer Arcangelo Corelli (1653-1713), and the first two kings of Italy Vittorio Emanuele II (r. 1861-78) and his son Umberto I (r. 1878-1900).