When we look at the architecture of the ancient world, progressing from the Greek temple, through such structures of the Roman Empire, as the Pantheon, to the Christian basilicas of the Late Empire, it is possible, even with a quick glance, to recognise that the architectural principles of the ancient world underwent an immense change. It has been termed 'a revolution in artistic taste'. Though perhaps it could be better described as a process of evolution.
Classical architecture concentrated on the exterior, and that is clearly demonstrated in Vitruvius' handbook on architecture, De Architectura: it is about symmetry and proportion, using a subtle rhythmical alternation of solid and void. In general terms, the change in the principles moves towards an acceptance of illusionism and an expression of intangible special effects. The new concept was made possible by concrete, which could be used as an envelope to enclose space, so that buildings could be released optically from their massive bulk. So where does the Pantheon fit into this development?
We Finally Know How Ancient Roman Concrete Was So Durable: https://www.sciencealert.com/we-finally-know-how-ancient-roman-concrete-was-so-durable
The historian and archaeolgist, Bryan Ward-Perkins, gives an answer, “the Pantheon is perhaps the first major monument to be composed entirely as an interior”. The exterior is conditioned by the interior.
The central structure, a ring of solid masonry is externally concealed by a traditional porch and internally the immense wall surface is broken up by exhedra and niches, giving no hint of the elaborate device for taking the thrust (weight) of the dome. The architect has created a vision of organic space within the building.
The original Pantheon was built by Marcus Agrippa as the inscription on the outside demonstrates, M.AGRIPPA.L.F.COS.TERTIUM.FECIT = Marcus Agrippa, the son of Lucius, three times consul, built this, (though the metal lettering on the inscription is modern). Agrippa's temple was destroyed by fire in CE 80; it was rebuilt by Domitian but perished again sometime during Trajan's reign. From the evidence of the brick stamps, the present structure was built sometime between CE 118 and 128 during the reign of Emperor Hadrian. His building seemed to have survived virtually intact. Though there are two inscriptions that provide evidence that restorations were carried out by Septimius Severus and his son Caracalla.
In the field of architecture, as in any art, it is an obvious truth that the way in which men design their buildings reflects, however unconsciously, their view of the world in which these buildings arise, and also mirrors their concept of the relationship of humans to that world. The architect, though he may deliberately attempt to create a new and unique edifice, is in some measure, inextricably confined to the spirit of his age. Thus, for more than a century, the full potential of concrete was not realised in Roman architecture.
There is difficulty in understanding the exact nature of Agrippa's building. It seems, however, most improbable that it, in any fundamental way, resembled Hadrian's construction. Augustan architecture (1st century CE) tended to revert to classical canons. To focus on faultless proportion, perfection in taste and attempted in its constructions to capture a mood of peace and order. In this period art and architecture were produced as propaganda to endorse a concept of stability that an exhausted Roman world, after a series of civil wars, so badly needed. It does not seem possible that the revolutionary design of the Pantheon belongs to that era of serene poise. For this reason, it is certainly tempting to believe that the earlier temples were broadly rectangular in plan, as evidence under the present portico suggests: the slight angle on the modillions of the raking cornice on the pediment of the present porch suggests they were originally from a pediment that was not so steeply inclined. This has promoted the idea that perhaps Hadrian's porch incorporated part of Agrippa's pantheon which had a broader front – possibly decastyle (a temple or portico having 10 columns in front). One art historian has proposed that the earliest structures should be compared with the Temple of Concordia Augusta In the Forum Romanum dedicated. By Tiberius in CE 10.
The age of the Antonines was essentially a peaceful and serene age. The tensions of the empire that had underlined the feeling of insecurity for much of the first-century rulers had diminished as a firm foundation to the empire have been provided by decades of sound provincial government and military security. The world had become a 'coherent cosmos' expressed
politically by the belief in the Empire. This new universal concept of empire was linked and interwoven with 'the Greek revival' of the principate of Hadrian, an enthusiastic philhellene. The pedantic love of the archaic, which characterised so much of the current literature, did not stifle architectural concepts. There was no return to sterile classicism. The column, the architraves, those essential elements of the classical style were combined artistically and functionally with arcuated construction. and formed an 'indissoluble unity'. The classical orders had tended to become submerged but were now incorporated in vaulted constructions and became an integral part of the design. There was an amazing synthesis of two fundamentally different methods which represented the two conceptions of the time. An amazing synthesis. The Pantheon was a product of the spirit of this age.
There can be little doubt that the Emperor played an important part in the design of the monuments of his reign. Two anecdotes from the historian Dio Cassius, as recorded by Joannes Xiphilinus, concerning Hadrian and the Greek architect Apollodorus. Though they are of little historic value, they seem to confirm that Hadrian had some knowledge of architectural principles. It has been suggested in an interesting, if slightly fantastical, theory concerning, the Emperor command to the architect, "Be off and draw your pumpkins". It is suggested that the drawing was of a gored or umbrella-shaped dome of the type seen in several Hadrianic buildings. The vestibule of the so-called Piazza d'Oro, Tivoli is a fine example since the outer surfaces of the vault would have resembled a pumpkin. It would be quite within the character of the ubiquitous Emperor if he had a hand in the design of a Pantheon himself.
Externally, the Pantheon has few pretensions and it is difficult not to believe that the triple naved portico of the present building does not echo Agrippa's temple. The entrance porch is a trabeated construction with an octa-style front surmounted by a huge gable. It is unlikely that the pediment contained any statuary as it is too shallow; a bronze relief has been suggested. The entrance sits on a podium that was once approached by five steps but is now buried beneath the pavement. Some have criticised the portico: "at best it is unacceptable, only as an apology to tradition". However, while admitting that the portico today appears awkward, it acts as a visual servant of a radically new idea, a monumental interior.
The building in ancient times was not freestanding, as the baths of Neptune were attached to the south. The porch also would obscure the view of the dome owing to the lower level of the forecourt - much lower than at present. To the observer a startling antithesis would exist between the exterior and the interior, as no hints of the dome will be given from the outside.
Behind the portico stands a vast cylinder of brick and concrete. The exterior is likely to have been covered in stucco between the cornice, but there is a notable absence of putlog holes in the upper part. That perhaps suggests that the facade of plain brick was left undecorated. From outside, the cylinder and the portico form two separate components with the rectangular member containing the door and two niches for statues inserted between them as a link. This intermediate block , as suggested above, appears to have been designed to obscure the rotunda and so heighten the contrast between the exterior and the interior. It seems the method of joining the entrance to the cylinder was considered so successful that it was repeated later on the Asceplion at Pergamon in Asia Minor (modern Turkey).
Over the cylinder rises the mighty dome, a hemisphere beginning halfway up the height of the interior; following accurately Vitruvian principles the dome's coffers climb up five rings to an oculus, the only source of light in the whole building. Round the interior wall, run four rectangular and two segmental niches which are screened by columns. These together with the pilasters at the edges of the walls carry the circular architraves, whose strong horizontal line divides the wall into perfectly balanced stories. This is only broken in two places by the barrel vault over the entrance and the semi-dome over the apse, which is opposite the entrance. The niches give the appearance of minor alterations of shadow which also subtlely emphasize the central space.
The decorative columns supply the interior with a tangible substance, and the effect created is that these columns, the architrave and 'the delicately articulated architecture of the upper storey support the dome. This impression is strengthened by the fact that over the niches of the lower story and between the delicate pilasters of the upper there are two latticed windows through which light from the interior fell on the back walls of the niches (n the 18th century, this attic was replaced by a heavy stucco molding, though the one over the original attic has been restored recently). The result was that the walls of the building were like a transparent shell and the columns appear to take the whole thrust of the dome.
The visional effect is as if the rotunda's space is detached from the ground plane. However, this separation of structure and space is only internal and there is no hint of the articulation of the niches on the exterior surface beyond the arched brickwork. In reality, a complicated system of buttressing arches around the cylinder conducts the thrust of the dome onto eight massive piers within the wall. The principle is much the same as the vestibule of the Piazza d'Oro. One historian argues that the piers were "not so much to distribute the load and thrust as eventually compound the structure as to check the warping flow of its inert material as it set"; suggesting the building settled itself over time.
The interior of the cylinder was decorated in a veneer of various marbles that created a colouristic effect, greatly adding to the impression of organic space. The dome is covered in five rows of 28 coffers, diminishing in length and width as they rise to the oculus. This could be described as a compression ring that recalls the dome constructions found in Syria or the rock tombs at Alexandria. It is essentially a cut stone technique. It is tempting to equate Apollodoros' nationality with the introduction of such methods but there is no known evidence to confirm the connection. The exterior of the dome was covered in bronze tiles, which have now been replaced by led strips.
There has been much discussion and argument over the meaning of the dome. Dio, Cassius writes, "perhaps it has this name (Pantheon) because it received among the images that decorated its many statues of the gods, among them Mars and Venus". I favour the view that the name is because the dome of the Pantheon resembles the heavens. It has become interpreted as an astral cosmic dome. One architectural historian compares the Pantheon's dome with the vault of the Stabian Baths and the dome in the house of Caecilius Jucundus at Pompei, which are decorated with stars. It has, therefore, been suggested that the coffers were decorated with gilded rosettes so they represented the stars and the oculus was the sun. It could be that the dome was connected with some pseudo-cosmology that represented the secular mission of the Roman Empire.
Dio Cassius also states that Hadrian transacted the business of the state in the Pantheon. From this statement the ancient historian W.L.MacDonald has hypothesised, "The mysteries of the celestial mechanism and the planetary forces long identified with the gods were expressed in a design suggesting that all of these ideas and were inseparable from the persisting mission of the Roman state". This esoteric interpretation of the Pantheon symbolism is perhaps overemphasized in relation to its functionalism: where a large number of people could be assembled. At this time, however, it is too difficult to untangle the threads that led to the Pantheon's conception. Certainly to the observer, there is a strong argument for acquainting the cosmos effect of the interior with the universalism of Roman rule. The Pantheon is to Rome what the Parthenon is to Athens. They both symbolise a special splendour and grandness now, whether that was their intention when they were constructed or not.
Inspecting a crack in the Pantheon's dome, 1925 - love this image, which shows the incredible scale of the dome.
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