Temple, church, icon.
The Pantheon inspires two contradictory impulses: silence and speech. Both are provoked by the part of the building that most come to the Pantheon to see, the dome. Awesome in the true sense of that word, and an engineering marvel, it has the widest span of any Roman vault, and is still the largest unreinforced concrete dome in the world.
Medieval visitors discerned in its lofty weightlessness something satanic. Disturbed by its apparent levitation, resting on seemingly nothing, they dubbed the whole edifice a ‘house of devils’. The actual reason the dome stays up there, more prosaically, is concrete. And concrete, one quickly comes to realise, is what the Pantheon is all about. Concrete and geometry.
Few things are certain about the Pantheon – not its builder, its purpose or how it got its name. It was constructed on the Campus Martius – the field of Mars – outside the city walls on land developed only during the late-Republican era. The streets surrounding the Pantheon came later, assembled piecemeal after the collapse of the empire, when a shrunken population moved closer to the Tiber following the disintegration of the city’s aqueducts.
The dedication to Agrippa on the frieze is misleading. Agrippa’s Pantheon, the foundations for which are below the current structure, was built around 27 BC. Little is known about Agrippa’s building, aside from the fact that he wanted to dedicate it to Augustus and erect a statue of the emperor inside which, ever conscious of Roman sensibilities, Augustus refused. A statue of Julius Caesar (already divine) was placed inside as a compromise, and one of Augustus placed on the porch alongside Agrippa. The area around the Pantheon already had immortal associations, as it was here that according to legend Romulus had ascended into heaven; Augustus’ presence on the porch suggested he would soon be joining his illustrious forebears.
Agrippa’s Pantheon was seriously damaged in a huge fire in 80 AD. Domitian made restorations but the structure was again struck by fire in the reign of Trajan (r. 98–117). Date-stamped bricks now point to today’s Pantheon being constructed during his rule, and the mark Trajan left behind architecturally in Rome is still much in evidence in his eponymous market and column adjacent to the Forum. Following Trajan’s death, building continued under Hadrian, though confusingly Hadrian kept the original dedicatory inscription to Agrippa when it was completed around 125 AD.
The Pantheon’s intended purpose is still unclear. Its name – from the Greek pantheion (all the gods) – would point to a temple, but temples had altars out the front, and no such altar at the Pantheon has been found. Dio Cassius, writing in the second century, was himself unsure; he describes statues of Mars and Venus in Agrippa’s Pantheon, but suggests the name is derived from the vaulted dome as representative of the heavens. A temple comes closest to describing it, but perhaps not in the conventional sense of an abode of the gods. Some kind of dynastic monument to Augustus seems likely, a kind of underlining of his temporal power buttressed by divine association. The presence of his divine predecessor’s statue, the area’s connection to Romulus, and the fact the building is in perfect alignment with Augustus’ still extant mausoleum all point to this end.
Whatever its purpose, Agrippa’s Pantheon was not made from concrete. The great fire that swept through Rome during Nero’s rule (during which, far from idly fiddling through, the young thug was not even present to witness) inaugurated the widespread use of fire-proof, brick-faced concrete. It was in the decades following the fire that Apollodorus of Damascus built some of Rome’s finest monuments, including Trajan’s baths, market, forum and column. All share features with the Pantheon, and mark him out as most likely to have taken on a project of its size and importance. Trajan’s buildings were huge, concrete structures with domes and half-domes, porticoes and exedrae. None, however, contained anything as ambitious as the Pantheon’s dome.
Resting on a massive concrete drum, the dome is one of four elements that make up the structure, alongside the drum, transitional block and portico. One dome in particular is likely to have been influential. The Octagonal Hall at Nero’s Domus Aurea was a unique and widely admired structure with a concrete dome and oculus that permitted light from above. Like the Pantheon, it was lauded as an example of achieving the near-impossible in architecture and was crucial in demonstrating what could be achieved with concrete. Apollodorus is almost certain to have seen it up close when working on Trajan’s baths, which were built over the Domus Aurea.
The difference between the domes of the Octagonal Hall and the Pantheon is size, the Hall’s being far smaller. To bear the weight of the larger Pantheon dome, the building’s drum was packed with concrete more than 6 meters thick at its base. The 28 coffers on the dome (obediently narrowing in size on each ring) also relieved some its weight, along with the use of lighter materials like tufa and broken amphorae (shards of pottery) near the oculus, which itself reduces the total weight.
Domes have always been a daunting prospect for architects. Every aspect of a building is subject to one of the twin forces of compression and tension, but a dome is faced by both, compressing from above and tensing at the sides. These energies are channelled in the Pantheon to its thick concrete base, which was made by mixing the volcanic ash pozzolana from Mount Vesuvius with lime to produce an incredibly strong foundation to absorb the pressure. It was the use of substances like pozzolana, widely exploited by the Romans, that sustained the dome of Pantheon’s devilish levitation.
If concrete is the earthbound material that made the Pantheon possible, then it is geometry through which the Pantheon’s intellectual pleasures are unpacked. Extensive use of concrete established a vast space into which geometric shapes could form. A perfect sphere fits exactly from the oculus to the floor, for instance; far from being a mere curiosity, it reinforces the ‘divine’ nature of the building. Mathematical harmony represented the perfection of the universe, and, transposed into architecture, created ‘perfect’ structures. These ideas of Euclid and Archimedes (who discovered the formula for the perfect sphere) were incorporated into the Pantheon’s design, from the 28 coffers on the dome (28 being a perfect number, equal to the sum of its factors) or the circle/square arrangement of the pavement. This interplay between space and geometric forms is an aesthetic pleasure that can be enjoyed whether or not the viewer is aware of the manipulation.
The stolid ordinariness of concrete and its melding with cerebral geometry combine to create a building that is both bound to earth and yet responding to the heavens. Admittedly, a closer look at the Pantheon’s exterior still reveals flaws. Probably the most noticeable is the meeting of the portico and the transitional block behind it that connects it to the drum (or rotunda). There is a second pediment on this block, higher than the original on the porch, and it is thought that this is the height the portico ought to reach. The ‘compromise hypothesis’ is an attempt to explain the disparity, the theory being that something happened during construction – perhaps the sinking of the ships carrying the columns from Egypt to Rome – that resulted in the smaller portico we see today.
Taken in its entirety, the second pediment does little to detract from the Pantheon’s aesthetic achievement. The overall impression is one of complete confidence in design and execution, and again it is the dome that expresses this best. Anticipating the dim light of a Roman church, the beam of sunlight that dances across the coffers affords the visitor one of the world’s most dramatic interiors. Naturally, imitators are myriad and diffuse. Brunelleschi, 1,300 years after the Pantheon’s construction, studied the building whilst trying to conceive a dome for Santa Maria del Fiore in Florence. Later admirers were equally smitten. Take these rhapsodic reminiscences from a twentieth-century observer:
From the time I experienced this building – no description, picture or photograph did it justice – I became interested in its history […] For a short while I stood in this space (the rotunda) – what majesty! I gazed at the large open oculus and saw the universe and sensed what had given this space the name Pantheon – God and the world are one.
This the reverie of Adolf Hitler remembering his visit to the Pantheon. Hitler’s Große Halle – proposed but never built – was almost a direct copy of the Pantheon intended for Berlin. Its dome would have swallowed up the Pantheon’s, as well as St. Peter’s, many times over, and would have represented only the grandest of the Nazi’s prolific pilfering of Roman imperial iconography (and a rebuke to the gentle harmony of the Roman original). Like the Pantheon, it was to have a coffered ceiling, columns and niches, including at its north end a tribune from which the Führer could rant. The connection here between Agrippa’s Pantheon with its Augustan dynastic symbolism and Hitler’s ‘great hall’ is obvious, though it is difficult to imagine Hitler erecting statuary of anyone but himself.
The Nazi party were not the first to borrow from ancient Rome to solidify their power. One fascinating, and less grotesque, example is that of Italy itself in the decades that followed the unification of the peninsular. Early Italian governments saw in the Pantheon a potent and much-needed symbol linking their fledgling nation to its imperial predecessor. Whilst other countries could only ape the imagery of ancient Rome, ‘Italians had the inestimable advantage of being able to take possession of genuine antiquities’. The incredible preservation of the Pantheon made it more desirable than any other vestigial ruin in the city.
The obstacle facing the Italian state in its ambition to obtain the Pantheon came from a familiar adversary, the papacy, which had been in possession of the Pantheon for more than 1,000 years. Granted to Pope Boniface IV by the Byzantine emperor Phocas in the seventh century, and filled with the bones of Christian martyrs, the Pantheon was renamed Santa Maria ad Martyres (Saint Mary and the Martyrs) and, over the centuries, was stripped of its various furnishings, including infamously the bronze beams from the portico by the Barberini pontiff Urban VIII (hence the pasquinade: what the barbarians did not do, the Barberini did).
Various attempts were made by the Italian government to seize it from Vatican control. The papacy, still smarting from having its temporal authority snatched away by the upstart Italian state, were loath to acquiesce. The Italian government were somewhat successful, with the bell towers added to the Pantheon in the seventeenth century, which obviously identified it as a church, tellingly demolished. More contentious still was the goal of having the first king of a united Italy Vittorio Emanuele II buried in the Pantheon. Ultimately this was carried out, but the idea of converting it into his national monument never came to fruition.
Hitler’s obsession with building a new, larger Pantheon for Berlin, and the eagerness with early Italian governments tried to bring the Pantheon under their control, testify to the long, often strange, shadow cast by this unique monument in which the tyrant and the democrat, the secular and religious, have all claimed a stake. It remains, after nearly two millennia, a magnificent sight. To stand squinting at it in sun-baked Piazza della Rotonda is to know one has properly arrived in Rome; there it is, squatting like some lost civilisation’s temple in a forest clearing, hidden in a warren of streets. In continuous use since it was built, the Pantheon is a raw and beautiful emblem of human ingenuity and the inexorable passage of time. There are Roman structures bigger and taller but none as majestic.
 King 2000: 28
 I take absolutely no credit for these ideas, with which I continue to grapple. They derive from Giangiacomo Martines’ brilliant ‘The Conception And Construction Of Drum And Dome’ in The Pantheon: From Antiquity to the Present (2015). I owe a great debt to this book for this article.
 Wilson Jones 2015: 214
 Geisler 30: 1977
 Williams 356: 2015
Giesler, H. Ein anderer Hitler: Bericht seines Architekten: Erlebnisse, Gespräche, Reflexionen. From: ‘Volkshalle’ [wikipedia].
King, R. Brunelleschi’s Dome: The Story of the Great Cathedral in Florence. London.
Marder T, A, and Wilson Jones, M. The Pantheon: From Antiquity to the Present. Cambridge.
Martines, G. ‘The Conception And Construction Of Drum And Dome’. In: Marder T, A, and Wilson Jones, M. The Pantheon: From Antiquity to the Present. Cambridge.
Williams, R. B. ‘A Nineteenth-Century Monument For The State’. In: Marder T, A, and Wilson Jones, M. The Pantheon: From Antiquity to the Present. Cambridge.
Wilson Jones, M. ‘Building On Adversity: The Pantheon And Problems With Its Construction’. In: Marder T, A, and Wilson Jones, M. The Pantheon: From Antiquity to the Present. Cambridge.