Immediately after hearing that hallowed name images of domes, grand open spaces and columns are brought to mind (and porticos too if you know your terminology!). Few buildings have captured the imagination of the world quite like the Pantheon, with its unique architectural design, its many mysteries, and its sheer longevity.

If you’d yelled out ‘THE PANTHEON! when asked at trivia night ‘What’s the world’s largest un-reinforced concrete dome?’, you’d be right. But who designed it? What was it used for? And what’s with that big open hole in the top?

Well, fear not! Because once you’ve reached the end of this blog you’ll have the answer to all of these questions, plus the answer to the best Roman trivia question: How has the Pantheon managed to last so long?

Where to begin…?

Oh yeah, so, spoilers, but we don’t know exactly who designed the Pantheon.

Our best guess, based on the current evidence, is that the third and current iteration of the Pantheon was designed by Apollodorus of Damascus.

Wait … third you say?

That’s right! According to Cassius Dio, the Pantheon was first built in the Campus Martius under Marcus Agrippa around 27-25 BCE (Cass. Dio 53.27). This early Pantheon was very different in shape to the one we are used to today, missing the iconic dome on top.

The second iteration of the Patheon was the result of extensive structural damage caused by a fire in 80 CE, Domitian restoring it shortly afterwards (Cass. Dio 66.24.2). But the Pantheon could not catch a break, it was struck by lightning in 110 CE and once again caught fire, this time burning completely to the ground (Pauli Orosii 7.12; Tod & Jones 2015: 7). A Roman firefighter was certainly never short on work!

The version of the Pantheon we see today was built during the reign of the Hadrian, around 125-128 CE (SHA Hadr. 19). We have this date thanks to some cool brick stamping technology that has revealed it was not built during the reign of his predecessor Trajan, as had once been thought.¹

OK, but what was the Pantheon used for?

‘Wh-wh-whoa wait a minute, I’m only here for the answer to the social dynamite trivia question: what is it?’

Well, its Greek name would suggest that it was a temple for ‘all the gods’ – pan being Greek for ‘all’, and theoi meaning ‘gods’. But, Roman history is never that simple. The Pantheon has lived through some seismic cultural transitions and its function has shifted accordingly over the centuries.

Cassius Dio tells us that Marcus Agrippa initially intended for the Pantheon to honour Augustus, which, in turn, would have brought Agrippa legitimacy and honour (Cass. Dio 53.27.3; McEwen 1993: 56).

The version that followed during the reign of Hadrian is more contentious. It is often assigned the role of a temple, due to its size, grandeur and expense. However, all Roman temples were of a standard rectangular shape, which we’ve seen the Pantheon is not. Plus, the large circular opening at the top of the dome would have made regular services tricky.

It seems instead that Hadrian held a circulating court within the Pantheon as well as other buildings, as Cassius Dio helpfully recorded (Cass. Dio 69.7.1; McEwen 1993: 57).

So it was a pseudo-throne room?

More than likely, but other uses have been suggested. Christian historian Iulius Africanus wrote that a library was built in, or close to, the Pantheon in the third century CE (Thunø 2015: 231).

Although it certainly wasn’t limited to a scholarly function. The Pantheon’s intertwining with imperial dynasties continued into the 4^th^ century with laws said to have been announced there under Constantius in 370 CE (Thunø 2015: 231).

Following its conversion to a Christian church under the Emperor Phocas around 610 CE source material on the Pantheon is quiet. Perhaps the strongest hint that the Pantheon was used as a court or throne room through to the 7^th^ century is the Pope’s use for it after its conversion. Popes made regular visits to the Santa Maria Rotonda, as the Pantheon came to be known, holding services and feasts there. This became a means to extend the power and legitimacy of the Church to the masses throughout the world, with the Pantheon becoming one of many ‘stational churches’ (Thunø 2015: 231-3).

But how did they build it?

As with all ancient monuments of impressive engineering and architectural marvel, the burning question is: ‘how did they build that?’ and ‘how is the damn thing still standing today?’

To understand these questions, first we have to briefly discuss the design of the Pantheon.

Visitors to the Pantheon first enter through the portico, a very grand porch lined with three rows of columns. But these are not just any columns, they’re forty foot Corinthian granite columns shipped all the way from Egypt! (Ressler 2015). At the time of construction, a flight of stairs would have led to the portico, but later construction raised the level of the ground and the stairs were no longer necessary (Ressler 2015).

The vestibule links the portico to the main circular drum that is the Rotunda. Once inside, the Rotunda makes for an incredible sight, its windowless round walls, exactly 43 meters tall and 43 meters wide, form a perfect sphere! (see figure 6; Waddell 2015: 133).

From here, to marvel at the Pantheon’s grandest feature all you need do is look up! From the centre of the room you can see the famed, domed roof with it circular opening (Oculus) at the top, letting in all manner of weather, be it rain, hail or shine.

How many men does it take to change a dome?

Only a few good men it seems.

The answer may be surprising, but according to careful analysis and some quick maths, it is estimated that the Pantheon would have needed a minimum of 240 men on site each year of its nine year construction period (DeLaine 2015: 190). A poultry figure when its compared to the 4000 men required to build just the central block of the Baths of Caracalla (DeLaine 2015: 190).

And to the real question …

‘How does the Pantheon not topple under that massive dome?’

Well, it all comes down to two ingenious ideas that restricted lateral thrust.

The Roman concrete used for the bricks was made in an incredibly unique process. Mortar was mixed with lime and pozzolana (a volcanic powder found in the town of Pozzuoli), an exceedingly useful material because it could be cured in water without air (Martines 2015: 126-7).

Into this mix different aggregates were thrown, all with different weights and structures. the base of the dome had bricks with the heaviest aggregates – brick fragments. What followed were layers of concrete with increasingly lighter aggregate materials. First were brick fragments, then layers of tufa, followed by lighter tufa and lastly, pumice mixed together with volcanic slag (Martines 2015: 126-7). This process lessened the otherwise significant amount of lateral thrust the dome would have exerted onto the drum.

The honeycomb patterns (or coffers) and Oculus (seen in figure 6), while pleasing to the eye, served more than an aesthetic purpose. They again helped make the dome lighter to further reduce lateral thrust (Martines 2015: 127).

So are you ready for a Roman themed trivia night?

While you’re now well equipped to answer those big questions, it’s important to remember that today’s Pantheon is very different in content and aesthetics to what was originally built. The sources tell us that pieces, artefacts and statues in the Pantheon have been changed, removed, lost, or damaged over the centuries. This, in part, explains how the Pantheon has managed to survive as long as it has (Moore 1899: 40-3).

Successive generations have marvelled at its architectural uniqueness and symbolic importance, and kept it alive. As such, it shouldn’t be a surprise to learn that the Pantheon attracts 7 million visitors annually.

New rulers have come and gone in Rome, but the Pantheon remains standing.

Further Reading

A travellers blog with loads of pretty pictures of the Pantheon Interior, ‘A Singaporean’s Maiden Trip to Europe’.

A schmick looking 3D model of the interior of the Pantheon, put together by Mathew Brennan.

Roma Experience ‘The Imperfect Perfection of the Pantheon in Rome’.

Bibliography

Ancient Sources

Scriptores Historia Augusta 1921 trans. D. Magie, Harvard University Press.

Cassius Dio, Roman History 1917 trans. E. Cary, Harvard University Press.

Paulus Orosius, Historiarum Adversum Paganos 1882 ed. C. Zangemeister (Corpus Scriptorum Ecclesiasticorum Latinorum).

Modern Sources

DeLaine, J. 2015. ‘The Pantheon Builders: Estimating Manpower for Construction’ in T. A. Marder & M. Wilson Jones (eds) The Pantheon From Antiquity to the Present, Harvard University Press.

Marder, T. & Wilson Jones, M. 2015. ‘Introduction’ in T. A. Marder & M. Wilson Jones (eds) The Pantheon From Antiquity to the Present, Harvard University Press.

Martines, G. 2015. ‘The Conception and Construction of Drum and Dome’ in T. A. Marder & M. Wilson Jones (eds) The Pantheon From Antiquity to the Present, Harvard University Press.

McEwen, I. 1993. ‘Hadrian’s Rhetoric I: the Pantheon’ Anthropology and Aesthetics 24: 54-66.

Moore, F. G. 1899. ‘The Gilt-Bronze Tiles of the Pantheon’ American Journal of Archaeology 3: 40-43.

Ressler, S. 2015 ‘The Most Celebrated Edifice-The Pantheon’ Kanopy.

Thunø, E. 2015. ‘The Pantheon in the Middle Ages’ in T. A. Marder & M. Wilson Jones (eds) The Pantheon From Antiquity to the Present, Harvard University Press.

Waddell, G. 2015. Sources and Parallels for the Design and Construction of the Pantheon in T. A. Marder & M. Wilson Jones (eds) The Pantheon From Antiquity to the Present Harvard University Press.