The pantheon is an artistic and imaginative blend of three major architectural focus: the unification of traditional temple form and the new domed space, the technical development of concrete constructions, and the tendency to obscure construction and structural elements. This paper discusses the Pantheon by analyzing the architecture from various aspects such as its three distinctive spaces and the experience they brings, the lighting of the interior, innovation such as coffering, the skillful use of concrete, and the Roman’s attempt to conceal the construction.
Furthermore, the potential meanings and implications are evaluated by formal analysis and looking at the cultural context of the empire. Pantheon, with its revolutionary design, serves as a premium exemplar of the Roman architecture of Hadrianic times where the grand traditions of trabeated classical architecture are brought together with the more youthful vaulted style.
The building, completed in 128 CE, consists of three divisions of space—the more traditional columnar porch visible to the approaching visitors, the unconventional and innovative gigantic domed rotunda which most likely would be an astonishment to the spectators of its time, and the rectangular form which have been introduced as a transitional space between the porch and the rotunda. The approach to the building is commonplace: a long and narrow closed forum, at the south end of which stood a temple front created as a conservative gesture to satisfy the traditional expectations of what a temple ought to look like.
Originally raised above ground level, the porch resembling that of commonplace Roman temple is originally preceded by a flight of five steps. Continuing the classical tradition, the porch with towering, vertical forms features multi-leaved Corinthian capital, the corner columns are slightly thicker than the others, and there are many additional perspective correction in the carved detail of the marble entablature, recalling the visual correction in the Parthenon of Acropolis.
Yet the columns are unfluted and the entasis is such that its curve becomes flatter toward the ends of each column shaft, a rather baroque quality. An illusion of continuing interior longitudinal axis which in reality did not exist is thus created with the seemingly vernacular forecourt designed by Aggripa and the stable forms of the columned porch with its triangular pediment. While round buildings were not absent predating the Pantheon, the Pantheon is the first monumental public architecture with usable interior volume using domed space.
Relationships between the circle and the square, a subject deemed particularly interesting by the Romans, are explored in the design of the rotunda. Vitruvius, architecture commenter of Agrippa’s day, investigated and speculated about the proportions in both the human figure and architecture. Reciprocities are suggested between circle and the square, and the reach and theoretical envelope of an idealized human figure. In section, the rotunda is a semi circle inscribed in the upper half of a square with a lateral length equal to that of the diameter of the circle.
Namely, in three dimension, a sphere can be fit into the rotunda perfectly. One of the great challenge faced by the designer of the Pantheon is the transition and marriage of the orthogonal temple front and the curvilinear domed rotunda which seemingly do not form an integrated whole since it is inherently difficult to relate curving walls to a projecting entryway. The unification and integration of the two form is resolved with the introduction of a rectangular junctional space where the north-south axis created by the porch extend to be the radius of a circle.
The resulting architectural experience created by the three distinctive division of space is one that is most magical. Imbedded in dense urban context, what came into view is a quite traditional design. Yet once the spectator enters the rotunda, it is as if he has been transported to another world of the antithesis. This transition between spaces is also highlighted by the change in the quality of light from the bright court to the dim forest of columns, and then to the full and unimpeded lighting of the rotunda.
While indirect sunlight can enter the building via the north facing bronze door, the oculus, a 9 meter aperture in the domed roof, serves as the sole source of direct sunlight. Previous studies of the oculus in the Pantheon have emphasized its obvious structural role—it lightens the weight of the huge dome, thus reducing the risk of collapse. It has also been suggested that the roof opening helped cool the building during Rome’s blazing summers. Additionally, the fall of direct sunlight through the oculus into the essentially spherical building leads to comparison with a roofed sundial.
Whether formal similarity to a roofed sundial is deliberate or not, it must have been a deliberate choice that the light at the equinox should fall on the ceiling precisely at the base of the interior of the hemispherical dome, that is, on the dome’s equator, where the dome appears to end and the drum begins. However, to call the Pantheon a sundial would be inaccurate since no hours other than noon could be marked out in the building. Nevertheless, the element of the Oculus is definitely an indication of the cosmological importance of the temple.
The Oculus is the culmination and focus of the Pantheon as the entire structure captivates the gaze of every visitor and direct it to the heavenly opening. Offering no view of the exterior, mundane world, and isolating any disturbing noise, the space seems to be the portal to another world of a higher dimension—that of the heavens and gods’. The miraculous architectural experience of the dome can only be made possible by the Roman technological innovation of pozzolana concrete, the use of concentric stepped rings, the introduction of coffering and using concrete with different density to alleviate the weight of the dome.
The Pantheon introduces interior space as a fundamental expression a new existential dimension. The dome, with a clear span of 43. 3 meters, was unprecedented, nonpareil for well over a millennium, and not largely surpassed until modern use of steel and reinforced concrete. This remarkable scale is brought to fruition partially by a high-quality, “hydraulic” concrete which combines chemically with water and do not need to dry out as lime mortar does. The concrete will cure rapidly regardless of weather condition which makes it advantageous for massive, primary structural elements of large buildings such as the Pantheon.
Moreover, the compressive strength of pozzolana cement is far superior to that of lime mortar. The use of concentric stepped rings arrayed about the outer surface of the dome also contributed to the success of the dome. According to W. L MacDonald, “the rings add to the load over the critical or haunch portion of the great vault and function as buttresses, helping to bring the structure into stability through compression. ” In other words, the builders adds weight to direct the internal forces down the wall through the use of step rings.
Additionally, the engineer of the Pantheon took load off the dome by using the device of coffering, which forms a waffle pattern on the underside of the building beginning just above the springing and ending several meters from the oculus. The five diminishing row of coffers verging toward the oculus are related to the center of the floor and to the spectator who would stand there, demonstrating the Roman’s attention to human experience. Besides its structural purpose, the coffering on the inner surface is modelled to create a false perspective which makes the dome seems even higher to the human eye than it already is.
The observer only sees the revelation of all surfaces of the coffer at or close to the center of the floor. Seen from other perspectives, the edge of the pyramidal boxes begin to overlap, their recesses suggesting a greater depth than the hemisphere actually is. As the light angles in from the oculus, the surfaces of the coffers are revealed in a complex pattern of varying degrees of light and shade, creating a powerful illusion of looking into a deep whirling space toward its vortex.
Although the governing order of Pantheon’s structural system was based on a sixteen-part geometry, which is easy to layout, the twenty eight radiating column of coffering, multiplies of seven, rests diaphanously on the drum divided into multiples of eight to create dynamism. This move is intentional and necessary since if the coffering is aligned with the order of division of the drum, the rotunda would seem rather static. Likewise, the Roman explored different mixture of concrete and used lightweight aggregate in the upper reaches of the building, whose density is greatly less than that of the lower, supporting structure.
A variety of material is used to create the concrete which serves as the building’s structural support: traventine, tufa, brick and a light volcanic pumice. Due to concrete’s nature as an excellent material for compression and a poor material for tension, efforts have been made to decrease the load of the dome as it rises. The materials are employed in different combination so as to create a series of six layers, beginning with the heaviest at the bottom for compression and stability and cumulating with the lightest for the upper portion of the dome.
While the Pantheon is known for its massive concrete dome, the wall that support it and transfers its weight to the ground should not be disregarded for its graceful, elegant and intricate structural design. The ingenious and innovative construction of building is covered with ornamental articulation irrelevant to the structure and not exposed internally. Contrary to the misleading gracefulness of the interior wall, complex structural devices and masses of unseen concrete which supports the building is hidden beneath.
The wall, 6 meters thick, supports the 5000 tons of weight exerted by the dome. The wall is not solid but is more like a corrugated cardboard as it is riddled with stacked chamber. These chamber are beneficiary to the drying process of the concrete and also created eight load bearing area on the perimeter instead of a uniform distribution of load on the entire wall. Namely, beneath the cosmetic veneer and the camouflage, the rotunda is essentially a giant canopy supported by eight thick piers similar to the octogonal hall in Nero’s Golden House.
The series of vaulting ribs embedded in the wall of the rotunda is the pivotal element to the structural integrity of the rotunda. There are two systems of arches at work in the rotunda wall: the major 12 meter span arches which span between the eight piers and cover the niches visible on the interior, and the minor 5 meters span arches which are contained within the hollow piers themselves. A series of even smaller relieving arches further transfer the loads away from the architraves and onto the columns of the niches.
The loads placed on the supporting structure by the massive dome are thus carefully controlled. The great niches are screened by colored marble to eliminate architectural clarity. The columns seem to be supporting the high solid wall above while in fact unseen arches, vaults and masses of concrete serve as structural support. The polished marble surfaces of the first two zones, by reflecting light and making their substance hard to gauge, help to reduce the sense of the existence of the massive structure behind.
The treatment of the interior shows the imperial architecture’s desire for obscurity of the structure. While saying with precision what the meaning and purpose of Pantheon is impossible due to the lack of written evidence and inevitable subjectivity in the analysis of architectural form, attempts to tackle the mystery has been made numerous times due to the importance of the building. The commonly accepted theory is that the Pantheon is built as an cumenical temple dedicated to all the gods, not just of Roman tradition but of all roots and cultures.
This seems plausible since the Pantheon was created at a turning point in history when rites and rules drawn from a very long past were not yet abandoned, but the surge of a new and utterly different age was already being felt. Written evidence by Dio Cassius indicates that a statue of Julius Caesar, not deified for long, had been placed inside the original Pantheon. Additionally, statuary with patriotic and dynastic implications such as those of Aeneas, Romulus and Alba Longa etc. decorates the entire complex.
Seen in this light, it is reasonable to assume that the Pantheon contains not only the ancient and traditional gods, but also deities of recent origin and strong connection to dynastic and political meaning. On the other hand, it is easily imaginable that it related to cosmology. It has 7 niches for altars and statues and at that time there were seven known planets. The symmetry is perfect; the rotunda itself is divided into sixteen parts – a direct connection to the sixteen equal divisions of the Etruscan sky. The circle, the geometry generating both the plan and section of the architecture, is the most orderly and perfect of geometry.
It is without corners and without seams, and has no beginning and no end. It has been interpreted that this form which stands for continuity and security, is a metaphor in architecture for the dominion of Rome—the unity of gods, state, people, and the unity of the perpetual existence and function of the state with the never-ending revolutions of the planetary clockwork. The Pantheon, in this sense, represents the universe. Michelangelo the great painter of the Sistine chapel once described the design of the Pantheon as an “Angelic and not human design”.
Indeed, we can sense the divine immanence through observation of the diurnal path of the sun across the animated coffering, the elegant and complex wall which cleverly support the dome of perfect geometry. The rotunda is circular in form, endless and without seam like the empire which conceived it. The near perfection of the circular domed interior, utterly unlike anything previously seen on the earth, seemed to be the symbol and the consequence of an immutable union between the gods, nature, man and the state.