Pantheon

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The Pantheon is a domed Roman building on the Campus Martius in Rome, raised as a temple “to all the gods” and standing today as a Christian church. Its name is Greek — pan, all; theos, god — and it has remained roofed, walled, and in use for nearly nineteen centuries, which makes it the best-preserved major monument of the ancient city.

The structure now standing is not the original. Marcus Agrippa built a Pantheon on the site under Augustus, late in the first century BCE; the inscription across the portico still names him, though the building behind it is not his. After fire damage, the temple was rebuilt under the emperor Hadrian in the early second century — about 113 to 125 CE on the usual reckoning — and Hadrian, against his habit elsewhere, kept Agrippa’s name on the front rather than his own. What scholarship establishes from brickstamps is that the visible Pantheon is Hadrianic; the retained inscription has misled observers for centuries about its true age.

The dome is the reason the building matters to the history of architecture. Cast in unreinforced concrete, its coffered interior describes a perfect hemisphere whose diameter equals its height from the floor — a sphere set inside the rotunda — and at the crown a single round opening, the oculus, nearly nine metres across, stands open to the sky. It remained the largest dome on earth for more than a thousand years and is still the largest of unreinforced concrete. Light enters only through that hole and through the bronze doors, so the disc of sun tracks across the interior through the day like a slow hand.

What gods the temple served, and how, is less certain than the engineering. The dedication “to all the gods” is suggestive rather than documentary; the ancient sources say little about the cult conducted inside, and modern readings of the dome as a deliberate image of the cosmos — the heavens overhead, the planets among the coffers — are inference, attractive but unproven. The building’s later life is firmer ground. In 609 the Byzantine emperor Phocas gave it to the papacy, and it was consecrated as the church of Santa Maria ad Martyres — Saint Mary and the Martyrs — a conversion that almost certainly spared it the quarrying and decay that erased most pagan temples in Rome. It has functioned as a church ever since, and holds the tombs of the painter Raphael and of two kings of Italy.

The Pantheon thus carries two religions in one fabric: a pagan temple whose purpose is half-lost, kept whole by the faith that replaced it. The dome that was meant, perhaps, to gather all the gods now shelters a single one. The oculus has never been closed.

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