Temple dedicated to all the gods of Rome. Located in the Centro Storico of Rome, Italy, the Pantheon is one of the most beautiful buildings ever, anywhere.
The original Pantheon was built in 27 BC by Marcus Agrippa, one of Augustus Caesar's close friends and political allies. At that time, it was probably an ordinary temple (octostyle prostyle dipteral Corinthian, if you want it in technical terms). The marble columns and the inscription on the front dates from that time.
M AGRIPPA L F COS TERTIUM FECIT1
That temple burned down, was reconstructed, burned down again, and was rebuilt in its present form in 126 AD. There is persuasive evidence that the emperor Hadrian designed it.
Hadrian re-used Agrippa's porch2. Behind it, he added a barrel-shaped cella topped by a dome 44 meters in diameter, with an unglazed 9 meter oculus in the center. The dome's apex is also 44 meters from the ground, so that if it were extended into a sphere, the structure would be resting on the floor. Until Brunelleschi built the one in the Florence Cathedral in 1420-36, the Pantheon was the largest dome in the world.
Engineering a dome of that size at that time was a complex task. The main consideration was weight reduction, since unreinforced concrete can only bear a certain amount of load. The mix of concrete changes toward the top, with the heavier stone aggregate gradually replaced by pumice. To lighten the structure further, the outside of the dome is stepped, so that the roof is thinner at the top than at the bottom. On the inside, there are five rows of coffers, further reducing the weight of the ceiling.
The dome rests on a barrel-shaped structure, which uses three layers of brick arches to transfer the weight to eight massive piers. (This form is allegedly based on the structure of a pumpkin.)
Because of its distinctive architecture, the Pantheon fared better than most Roman temples when the Empire became Christian. It was transformed into the Church of Santa Maria ad Martyres, and is still used for Catholic worship today. Even so, many of the decorative features, such as the bronze roof tiles and marble facings, were stripped from it over the centuries.
The remaining interior decorations emphasize the difference between a traditional rectangular temple and the round dome. The marble floor uses a motif of circles within squares, while the coffers in the roof make a pattern of squares in a circular field. There are eight alcoves around the room, alternating between the trapezoidal and the semi-circular. Decorational niches on the load-bearing pillars are topped with either right triangular or semi-circular architraves. All of these contrasts underline how different this building is than all other temples in Rome.
Looking at it today, it's hard to appreciate the impact of the dome in ancient times. When the Pantheon was built, the street level in Rome was some 7 meters lower than it is today3. The temple had to be approached by a set of stairs. With that street level, anyone approaching the temple would have their view of the dome blocked by the building's porch. Furthermore, the streets around the Pantheon were so narrow and built-up that there was no angle of approach where the dome was visible. The unitiated wouldn't know about it until they stepped inside the building.
The impact must have been staggering.
- "Made by Marcus Agrippa, son of Lucus, in his third consulship" This allows the Agrippan building to be dated precisely, since we know the dates of all his consulships.
- Some archaeologists think that he rotated it 90 degrees in the reconstruction, and that Agrippa's temple faced north
- Street levels in ancient cities such as Rome tended to rise over the years from the accumulation of dirt and debris. The idea that street level will be the same from century to century has only come in since we've started paving all our streets.