Engineering Rome

Construction and Behavior of the Pantheon

By Alec Harrison‍


The Pantheon is one of Rome’s most iconic and best preserved ancient structures. With massive single stone columns holding up the portico at the entrance, the immense open interior space created by the cylindrical rotunda, and of course, the characteristic concrete dome and open oculus to top it off, the Pantheon is quite the engineering wonder to behold. However, the Pantheon as you see it today is not the Pantheon as it was when it was first built. Nor is it the first version of the Pantheon at that location. The Pantheon you see today is the third rendition of the “church of every god” that had been adapted and modified through the centuries. This is just one example of a piece of the Pantheon’s long history that includes unique ambitiousness, ingenious construction techniques, and examples of remarkable Roman engineering. Because of this rich, and often incompletely recorded history, the story of the Pantheon can be muddled with confusion and mystery. Yet because of its significance and breathtaking wonder, the Pantheon has been the subject of much study and analysis. While not all sources agree on every single point, the goal of this report is to try to sift through the many sources of information to examine some of the history, construction techniques, and evolution involved with its history, in order to better appreciate the marvel that is the Pantheon.

The Pantheon Today (Photo by author)
Telescopic view of the interior of the Pantheon (
Telescopic view of the interior of the Pantheon (

History of the Pantheon

The Pantheon is a breathtaking sight simply at first glance. Walk around a corner on a what seems like a typical Roman street and all of a sudden you see the massive columns inviting you in to the towering dome overhead. While it is great to look at and admire the dome, when you start to analyze and breakdown all the engineering involved with its construction, it only gets more impressive. To put it in perspective, the Pantheon is still the largest diameter unreinforced concrete dome in the world, meaning there is no reinforcing structure in or around the concrete, such as the rebar that would be used today. Still, after nearly 2000 years, it holds that record. The tallest building in the world changes about every 10 to 20 years, but the Pantheon has held its record for nearly 2000 years. That alone is a testament to the quality of the Roman engineering techniques that went into creating the Pantheon. After discussing some background information in the next sections, I will present some information to expose some of these techniques and methods that allowed for the creation and survival of the Pantheon.


While it is difficult to determine exactly who built the Pantheon, how, and when, there seems to be a majority consensus on the history as follows. In the year 117, Hadrian began the tremendous undertaking that was the construction of the Pantheon. He was in fact, rebuilding a church on the same site that the first two Pantheons where previously built upon. The first version, built by Emperor Marcus Vipsanius Agrippa, was said to have been a T-shaped building, constructed around 27 BC and burned down in the fire of the year 80. Rebuilt by Emperor Domitian, the second Pantheon was struck by lightning and burned down again in the year 110 (Parker, 2009). When Hadrian set out to rebuild the Pantheon again seven years later, the resulting plan included the ambitious 43 meter diameter dome.