Our Home in Rome is the Dome

By Kara Gustafson

“There is something in the immensity of the Pantheon that makes me fall silent. Standing beneath its dome as it soars above me, I marvel at its perfection. How did ancient man form these perfect recessed squares in the cement of the dome? How could it have been done aloft, and not on the ground, the dome turned on its back like a great turtle while humans scuttled around inside it like so many ants? It defies description; my words fail me, and rather than use paltry and insufficient ones, I prefer just to stand in awe and look”

Christine Engelen, student 2019

“When I walked into the Pantheon for the first time I was absolutely amazed. The architecture, art, and colors inside are absolutely stunning”

Emily Nardone, student 2019

“I don’t think anything will top dancing around the Pantheon at 3 AM in the pouring rain”

Marlena Giannone, student 2019

Top Left to Right: Students dancing in the night downpour from the steps of the Pantheon, lightning illuminating everything ; Carmyn G lovingly embracing a granite column ; The inside of the Pantheon including the oculus

Bottom: View of the Pantheon during night thunderstorm with lightning behind

I did not know what the Pantheon was. From the revered way it was mentioned, I knew that it was an impressive part of the city. On our first walking tour of Rome, we paused at an important elephant statue we discussed in our film class. Then, Julia pointed to a building that made up the next corner. 

“There it is! The Pantheon!” 

Unassuming and fading into the background of the surroundings were the brick sides of a curved building. As we slowly made our way to the front, my eyes grew wider and my mind ceased normal function. From what seemed to be an ancient pile of rubble grew dense granite columns stretching sky high, and rich marble floors leading our way into the sacred area. The long doors that open into the building seemed grand by themselves, and the light from outside bounced off of the marble surrounding the entrance. As we walked into the building, it felt as though a portal into another dimension had sprung out of thin air. 

Encompassing like a large egg, the building stretches upwards, intricate symmetrical marble decorating every surface. The ceiling is mesmerizing with rectangular recesses cut geometrically around the domed ceiling. In the center of the dome is a wide hole, letting in a beam of sunshine, lighting the inside of the building. 

Nothing has ever taken away my breath so fully. For the time that we were inside, the outside world was stripped away, and we were left standing in awe. The history of the building felt like it crept up the domed walls and compressed in on me. The intense presence of the building was suffocating. Every time that we have returned, it pulls us in. 

The Pantheon is the home of Rome to us, and no matter where we are wandering, we always end up turning a corner and stumbling upon it. From finding it flocked with tourists to spending long pensive afternoons staring upwards, it is the center of my adventures. From learning more about the history of the building to dancing in a downpour in the shadow of the pillars, it has marked our memories forever. 

History 

The site of the Pantheon was planned far before the current building was standing. It underwent multiple cycles of being built, catastrophically burnt, and then rebuilt again. The final form was built by Emperor Hadrian, known as Hadrian the Architect, in 125 AD (Low, 2). The name, Pantheon, is developed from the original dedication to many ancient gods. Pan, meaning “all”, and Theos, meaning “gods”. After Rome changed from polytheism to Christianity, the Pantheon was not used until the 600s, when it was reopened as a Christian church, where it still has mass.

The Dome’s Influence

The dome of the Pantheon, the part that makes it memorable to all who visit, has been immensely influential on other architects around Italy and the world. For example, the Duomo in Florence, making up the very recognizable silhouette of the city, was created by Brunelleschi and was inspired by the creation of the Pantheon. Another example of a notable Italian dome is Saint Peter’s Basilica in Vatican City. As a group when we received a tour of the museum and Basilica, our lovely tour guide explained that the lead architect, a well known man, Michelangelo, did not want to overshadow the prowess of the Pantheon, and therefore creating the Basilica to be one meter shorter than originally told, one shy of the height of the Pantheon (Low, 2).

Until the 20th century, the Pantheon was the largest concrete structure in the world. Despite being built in 125 AD, 1,893 years before this blog was published, it is still the world’s largest unreinforced concrete dome (Low, 2). What makes the Pantheon’s architecture so majestic? Standing in the middle of the room, it feels almost as if no one but the many gods of old could have created such a masterpiece. 

Engineering

Cement

Roman cement is typically called Roman Pazzolana. This cement is different from the norm of mixing limestone and sand which requires to be dried. Pazzolana is instead made by using similar chemical bonding methods to commonly used modern Portland cement (Mark and Hutchinson, 3). The Pantheon was built with different layers of cement, growing lighter as the structure got taller. This allowed the weight to be lessened. Towards the top of the structure, volcanic pumice, a light and strong rock, was used. Below is a figure showing some of the different layers of cement. 

Figure 1: Masi (5)

Domes 

The basic structure of a dome can be seen as a simple arch that has been spun around to create a dome shape. Due to gravity and weight issues when creating this perfect unsupported dome, the top of the arch, called the keystone, must be removed, therefore creating the oculus in the Pantheon’s dome. The fundamental forces within a dome are called the meridional and hoop forces. The meridional forces work longitudinally while the hoop forces are laterally (Low, 2). These forces are key in keeping domes standing, and an understanding of how their basic principles work is necessary to analyze the structure. The meridional and hoop forces especially allow domes to be built ring by ring from the bottom towards the top. 

Figure 2: Mark and Hutchinson (3)

Figure 3: Low (2)

Cracks

Due to the building’s age, it is not perfectly built. There are signs of wear and fatigue on the structure, resulting in cracks running vertically on the dome. These cracks are thought to be caused by the shrinkage of the cement. Another conclusion presented by Mark and Hutchinson in an early yet remarkable analysis of the building is that the cracks spreading upwards along the dome were unavoidable. The Romans built this structure after trial and error over millennia of past experience. They knew that with the cement, shape, and size, that the cracks would appear. The architects compensated by knowing that this would force the dome to be intrinsically a set of half arches (Masi, 5). The study on the development of the cracks spreading through the dome is a substantial field, as more analytic techniques are discovered using 3D modeling and force calculations. These studies are aimed at understanding the life of a structure such as the Pantheon as it is the oldest and largest, and applying these findings to current day modeling. 

Symbology & Architecture 

The physical structure of the building is impressive. One of the most remarkable qualities is that it contains almost a near perfect sphere, one of the most universally loved and romanticized shapes. This symbol can be traced to represent the world in its spherical shape. The only source of light is from the oculus, the circular opening at the top of the dome, possibly representing sun and moonlight. The dome can be broken into 5 rings, each with 28 coffers, the rectangular recesses to lessen the weight of the dome. This can be linked to the 28 phases of the lunar cycle (Fletcher, 1). The possible geometry mixed with symbolism continues when considering the ancient celestial objects: Sun, Earth, Moon, Mercury, Mars, Venus, Jupiter, and Saturn. This representation of eight is seen geometrically throughout the building with a fundamental positioning of concentric circles and squares. Below is a figure showing this placement. For more reading, see Rachel Fletcher, (1).

Figure 4: Masi (4)

Figure 5: Fletcher (1)

Conclusions

As one could imagine, the technical planning that must go into any sound structure is mind boggling. Especially when analyzing historical landmarks, it is difficult to theorize a story of the building. How was the Pantheon built exactly? Why did the cracks form? The analysis of the building has changed over time from speculation, to 3D modeling, to laser analysis of the building. Here I only briefly skimmed over the tip of what is a deeply rooted and intensely studied area. The articles I referenced go into much more depth about the subject, and are where I borrowed all figures from. All the credit belongs to the rightful owners of the figures, as well as the ideas referenced. The Pantheon has been considered by many to be the core of Rome. I understand this now. The Pantheon with its warm whispers and resonance of history is the beating heart of Rome. And to us Ragazzi in Rome, it has become a home. 

Arrivederci, Roma. 

About the Author 

Kara Gustafson is a Mechanical Engineering major at Colorado State University with a minor in History. Originally from Boulder, Colorado, she enjoys being in nature and studying the mechanics behind it. During her summer in Rome, she was entranced by the Pantheon and many other ancient buildings. She wants to thank her family for supporting her passions in every way possible, and her friends for being by her side through it all. The crowded trams, scramble to bag at the market, Flike dogs, smooth cappuccinos, Roman memes, and hang drying laundry in the Roman sun on the patio created a new routine for her, and she will always have Rome and her time here in her heart. 

References

(1)    Fletcher, Rachel. “Geometric Proportions in Measured Plans of the Pantheon of Rome.” Nexus Network Journal: Architecture & Mathematics, vol. 21, no. 2, Aug. 2019, pp. 329–345. EBSCOhost, doi:10.1007/s00004-018-00423-2.

(2)    Low, Kristina N. “Engineering the Pantheon – Architectural, Construction, & Structural Analysis.”    We’re Never Far from Where We Were, Brewminate, 5 Dec. 2017, brewminate.com/engineering-the-pantheon-architectural-construction-structural-analysis/.

(3)    Mark, Robert, and Paul Hutchinson. “On the Structure of the Roman Pantheon.” Art Bulletin, vol. 68, no. 1, Mar. 1986, pp. 24–34. EBSCOhost, doi:10.2307/3050861.

(4)    Masi, F., et al. “A Study on the Effects of an Explosion in the Pantheon of Rome.” Engineering Structures, vol. 164, June 2018, pp. 259–273. EBSCOhost, doi:10.1016/j.engstruct.2018.02.082.

(5)    Masi, F., et al. “On the Origin of the Cracks in the Dome of the Pantheon in Rome.” Engineering Failure Analysis, vol. 92, Oct. 2018, pp. 587–596. EBSCOhost, doi:10.1016/j.engfailanal.2018.06.013.

FINE

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