Entering the Pantheon is an experience that surprises even those who have seen it a thousand times in photographs. After the columned portico, the space suddenly opens into a circular hall covered by an immense dome, with a single opening at its centre through which the sky can be seen. No windows, no columns holding up the vault: only a great void shaped by geometry. Few buildings in the world express so clearly the idea of a temple as an image of the cosmos.
A temple for all the gods
The name Pantheon comes from Greek and means «of all the gods». The building we see today was rebuilt under the emperor Hadrian in the second century AD, on the site of an earlier temple commissioned by Marcus Agrippa. On the front of the portico one can still read the inscription attributing the work to Agrippa: Hadrian chose to keep the name of the first builder.
The historian Cassius Dio, writing in the third century, suggested an explanation of the name linked to its form: perhaps, he observed, the building was so called because its vault resembles the heavens. It is one of the oldest symbolic readings of the monument.
The inscribed sphere
The geometric secret of the Pantheon is simple to state. The diameter of the circular hall equals the height from the floor to the top of the dome: both measurements are about 43 metres. It follows that a perfect sphere could be inscribed within the building, touching the floor at one point and the dome across its whole surface.
| Element | Form | Symbolic value |
|---|---|---|
| Dome | hemisphere | vault of heaven |
| Cylinder of the hall | circle extended upwards | inhabited world |
| Oculus | open circle | sun, eye of heaven, passage |
| Ideal sphere | perfect figure | totality of the cosmos |
The lower part of the building is a cylinder as high as the radius; the upper part is a hemisphere. The circle, the figure without beginning or end, dominates every aspect of the plan and elevation.
The oculus: the sky inside the temple
At the top of the dome opens the oculus, a circular opening about nine metres across, with no covering at all. It is the hall's only source of natural light. When it rains, water falls onto the floor, which is slightly convex and fitted with drainage holes.
The oculus turns the interior into a kind of sundial. During the day a disc of light moves slowly across the walls and the dome, following the path of the sun. Some scholars have proposed that the disc lights up the entrance at noon on particular dates of the year, such as the traditional date of Rome's founding, 21 April; it is an interesting hypothesis that links the temple to the calendar and to the figure of the emperor entering the building bathed in light.
The coffers and lightness
The inner surface of the dome is carved with five rings of coffers, twenty-eight per ring, which decrease in size as they rise towards the oculus. Besides creating a perspective effect of depth, the coffers lighten the vault.
The Roman concrete used for the dome was mixed differently according to height: heavier at the base, lighter towards the top, where materials such as pumice were used. The thickness of the vault decreases progressively. Thanks to these choices, the dome of the Pantheon is still the largest unreinforced concrete dome in the world.
From temple to church
The Pantheon owes much of its preservation to its conversion into a church. In 609 Pope Boniface IV consecrated it to Christian worship as Santa Maria ad Martyres. The temple of all the gods thus became the church of the Virgin and all the martyrs: a transition that preserves, in a sense, the idea of a sacred totality gathered under a single vault.
Today the Pantheon holds the tombs of illustrious figures, including the painter Raphael and some kings of Italy.
How to visit it with a symbolic eye
Anyone entering the Pantheon can make a few simple observations:
- Stand at the centre and look up at the oculus, noticing how the space seems to revolve around that point.
- Follow the disc of light on the walls and note its position according to the hour.
- Feel the transition from the rectangular portico, with its columns, to the circular hall: from the ordered world of man to the space of heaven.
- Observe the coffers converging upwards, guiding the eye from the many to the single central void.
Studio Esoterico Cornelio considers the Pantheon one of the highest expressions of Western sacred geometry: a building in which the circle is not decoration but the very structure of space, and in which the centre is not an object but an opening towards the light.
In short
- The Pantheon was rebuilt under Hadrian in the second century AD, keeping Agrippa's inscription.
- Its interior diameter and height are equal, about 43 metres: a perfect sphere can be inscribed within it.
- The oculus, the only source of light, turns the interior into a sundial that follows the sun.
- Coffers and concrete that grows lighter towards the top make the great dome possible.
- In 609 the building was consecrated as the church of Santa Maria ad Martyres.
