The Pantheon is a rare, ancient building in Rome because it has resisted the decay of time so well. One reason it is such a treasure is that it is the only intact example of the architecture of the date of that size, age, and span. The ability of The Pantheon to hold up for centuries is no accident rather, it reflects a genius of engineering skill.
Many designers have copied and even equaled the fantastic design of this building, but none have done better at introducing true innovation in architecture as the Pantheon did. This is more phenomenal when you take into account that the building was designed in 125 AD under the Roman emperor Hadrian.
The basic design is one that is brilliantly simple, placing a round enclosure next to a rectangular entryway. The gateway to the Pantheon is built in the style of a Greek portico, using columns made of granite and finished off with a triangular pediment on top. The entrance is supported by three rows of 39-foot Corinthian columns. Eight of those supports are at the front and then there are two sets further in – each with four supports that lead you onward toward the central rotunda. So the rectangular section serves the function of joining the building and the portico.
The geometric simplicity of this design also displays many layers of sheer architectural brilliance.
One of the most noticeable sections of the building is the enormous concrete dome that is the roof of the building. This component of the Pantheon is so well designed that in any other architecture, that big dome would have come crashing down ages ago.
That awe-inspiring dome is 142 feet across, which makes it 46 feet bigger than the dome over the White House in the USAs capital city Washington. The ocular at the crown of the dome is 25 feet across. And that Oculus is the heart of the genius of that dome’s engineering and construction design.
It’s easy to think that the opening in the center of that large oculus is just for artistic design. But it has an outstanding job of reducing the weight of the dome. It is also perfectly balanced to distribute the stress of the dome’s weight around its circumference. This makes the dome as resistant to being crushed by a bicycle wheel that we are familiar with.
Despite helping to keep the dome aloft, the oculus allows in a soft natural light which illuminates the interior beautifully. It also allows leakage of the rain, but the designers made a slope of the floor, so water goes naturally away from the center to a drainage system in the perimeter, so a pour does not create a significant problem.
Along with the Oculus, the tapering steps used in the dome’s design provide more insight into the genius that was at work by the designers of the dome. The dome is thickest at the base where the thickness is 20 feet and made of heavier material than at the oculus where the thickness tapers to 7.5 feet which cause the dome to center and rest on that weight without creating excessive stress on the structure. This kind of engineering might be routine today but seeing such advanced engineering knowledge at work thousands of years ago is awe inspiring.
The result is building so stable that 2000 years since it was first made, the stability of the structure is rock solid. But that balance was designed and constructed without any modern tools or devices we associate with building today.
Now you add to that limitation the fact that the creators of the Pantheon had to work with relatively “primitive” means of transportation and the success is even more impressive. Every pound of building materials for this amazing building had to be floated to the site down the Tiber River and then laboriously moved to the construction site by cart using nothing more than human or animal power.
The massive bronze doors of the Pantheon have undergone some restorations over the years. But there has never been any serious structural repair needed or done to the Pantheon at any time. That record is even more amazing considering that the Pantheon was built on marsh land.
A good comparison regarding the incredible longevity of the Pantheon is the Leaning Tower of Pisa which seems to need virtually continuous effort to support and maintain that structure. Much of the reason for the troubles of that tower is the marshy ground under construction. Another great building that was built at the same time as the Pantheon in Rome is the Parthenon in Greece, and it is for all intents and purposes a wreck 2000 years after it was built.
In the eighth century, the Roman Pantheon became a church, and it is a functioning house of worship down to modern times. Unlike other buildings of similar age, the Pantheon continues to be as much a working building as it was the day it opened.
It is such a design marvel that the Pantheon has become a template for great engineering for numerous modern projects including the University of Virginia’s Thomas Jefferson Rotunda and the British Museum Reading Room.
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