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The uncanny architecture of the Roman Pantheon

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The construction of the oldest building in Rome is still a mystery to experts.

There are few Roman buildings to have survived the 2,000 years since the height of the Roman Empire, but only one has done so without some form of preservation effort: The Pantheon. Although it was rebuilt several times due to fires in the first century, the final iteration, constructed under Emperor Hadrian, is the same one that has stood in Rome for the last 1,900-years.

Originally constructed as a temple to all of the Roman gods, it was converted to a Catholic church in the early 7th century. Prior to the world’s social isolation, the Pantheon held weekly Mass, as well as holiday events, but the largest draw for this tourist attraction is in its cultural and architectural significance. The artist Michelangelo, upon first viewing the Pantheon, commented that it seemed more the work of angels than of man.

The oldest building in Rome, today the Pantheon stands as a monument to ancient Roman ingenuity and a puzzle of history. No one is sure exactly how the Romans were able to construct such a large-scale dome, although we’ve figured out a few of their methods, such as reinforcing the walls with supportive arches and the creation of an even more advanced form of concrete than we use today.

The most striking feature of the Pantheon is the massive dome, which was the largest in the world until the construction of the Florence Duomo in the late 13th century. The Pantheon, however, is still the largest unsupported dome in the world.

The impeccable concrete dome has a diameter of 142 ft. and the distance from floor to its apex is also 142 ft. This means that the room could hold a perfect sphere, an architectural feat of such precision that has left experts grasping at straws to explain its unprecedented construction. One theory holds that the concrete dome was poured in a single piece which was then raised over the supporting walls of the Pantheon. This, however, only creates more questions as to how this feat could have been achieved.

While we are unsure of how the dome was erected, experts have identified the materials used in the concrete mixture, which explains part of their method, at least. The Romans used a modern architectural practice called gradation, which saw the heaviest, strongest materials like large basalt rocks put on the bottom of the cement mixture, with much lighter pumice used in the uppermost sections. The concrete also becomes thinner the higher it goes up, so as to take some pressure off the base.

At the crest of the dome is an opening known as the oculus (or the Eye of the Pantheon), which is the building’s sole source of light. The sunlight refracts across the many marble surfaces inside the Pantheon to illuminate the entire room. This 30-foot circular oculus also helps the structure to stand by keeping weight off, and although rain can make it through the opening, the floors are ever so slightly slanted to allow for run-off.

Eitch Borromini notes that the interior is lined with 16 Corinthian supports that are nearly 40 feet tall and 5 feet thick. They were brought from Egypt through an extensive effort, which the travel website describes in great detail:

These columns were dragged more than 100 km from the quarry to the Nile river on wooden sledges. They were floated by barge down the Nile River when the water level was high during the spring floods, and then transferred to vessels to cross the Mediterranean Sea to the Roman port of Ostia. There, they were transferred back onto barges and pulled up the Tiber River to Rome.

The oldest part of the Pantheon, which historians believe dates back to its original pre-fire form, is the marble facade, which still bears the name of its original architect, Agrippa. That the name was allowed to remain on the facade is thought to be a sign of respect on the part of Emperor Hadrian.

While we are isolated from the world’s many wondrous sites, the Pantheon is still open to explore by means of virtual tours. There are several of these 360-degree views available of both the interior and the exterior of this storied building so that virtual tourists can see every inch of the Pantheon.

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