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1.10. Interior seen along main axis. (Photo Maxim Atayants)
The paving of the interior consists of a pattern of circular disks and squares that reinforce the essential geometrical themes of the whole building. Framed within 10-foot squares and separated by 3-foot bands, these squares and circles alternate with each other on the cardinal axes, as they do in all rows parallel to the cardinals. As a result, sequences of either squares or circles run along diagonal rows with a line of disks traversing from one diagonal exedra to its opposing mate, and with a single roundel suitably locating the absolute center of the composition.
The interior elevation consists of three zones, or ranges. The lowest incorporates the main columns and pilasters standing on the pavement and capped with a full entablature, and its prominent cornice extending around the girth of the fabric, broken only at the entrance arch and the main apse. The middle, or attic level, occupies the rest of the wall up to the springing of the dome. Finally, the uppermost zone consists of the coffered dome. A major unifying compositional feature is the use of prestigious colored marbles. The eye revels in what is in effect a “pantheon of marbles.” Their varied and distant provenance – from modern-day Egypt, Greece, Turkey, and Tunisia – provides a visual reminder of the ample reach of Rome’s imperial dominion, its unity, and its collective wealth.26 The majestic Corinthian order provides another unifying theme for the interior and for the entire building. Corinthian columns with monolithic shafts measuring 30 feet high – three-quarters the height of those in the portico – screen the exedras from the central space. But rather than the smooth granite of the exterior shafts, these are fluted and made of colored marble: purple-veined ivory-colored pavonazetto from Turkey and salmon-honey-colored giallo antico from Tunisia in alternate exedras.27 Pilasters rather than columns are employed to face the edges of the structural piers, in the middle of which are aedicules that must originally have housed some of the statuary in the building. In keeping with a sophisticated play of symmetries, the aedicules are of two types: those with triangular pediments were made of paler marbles while those with segmental pediments had a deep-hued polychromy. The columns and their pilasters carry Corinthian capitals whose marble, like that of the small pediments, comes from Carrara, the only stone employed in the Pantheon to come from Italy. The choice of this particular marble reflected its ability to hold very fine detail; indeed, these capitals are wrought with exquisite workmanship and such extraordinarily crisp finishing that they convey an almost metallic quality (Fig. 1.11).28
1.11. Corinthian capital from the interior. (Photo Maxim Atayants)
It is important to remember that the Pantheon presents today’s visitor with a mixture of ancient materials and modern repairs and replacements. Some of these interventions are easy to identify, such as the coffering and other embellishments in the principal apse and of course any feature related to Christianity. In other cases, the ancient elements and their subsequent replications are less easy to distinguish. Detailed inspections and technical analysis during a campaign of conservation under the direction of Mario Lolli Ghetti in the 1990s have revealed the full extent of the renovations of the seventeenth and eighteenth centuries, when a substantial proportion of the ancient revetment was replaced with thinner sheets of marble (often reworked ancient material) bonded to backing slabs of coarser stones. In Lolli Ghetti’s estimation, roughly two-thirds of the floor is either modern or ancient material that has been relaid in modern times. Here and there are stones not known to antiquity, such as pieces of giallo senese from the environs of Siena, which replaced damaged portions of the more fragile giallo antico. Nonetheless, the general pattern of the pavement and its polychromy have been faithfully maintained.
Sadly, this is not true of the elevation of the rotunda. Ancient materials were removed not just because they had become damaged but also because they were wanted elsewhere. As Arnold Nesselrath’s Chapter Nine makes clear, the prized porphyry shafts on the aedicules of the piers have been robbed and replaced with columns of either paler reddish rosso antico or gray granite, the latter representing a rupture with the intended color scheme. Similarly, revetment made of serpentine, also known as green porphyry, was substituted with the more common but less intense verde antico. The most radical modifications occurred on the attic level of the interior. Here, the alternating panels framed by ornamental moldings and pediments over window-like recesses can be firmly dated to 1753, when the ancient composition was heavily altered. The original scheme, which appears in the sketches of early modern antiquarians and in Giovanni Paolo Pannini’s views, as well as a small section of the present attic reconstructed in the 1930s, consisted of little pilasters (or “pilastrini”) arranged in groups of four to either side of the “windows” above the exedras of the building. The fact that the pilastrini were not aligned in predictable fashion either with the columns below or the ribs of the dome above contributed – like the junction of the portico and rotunda on the exterior – to the theories about successive building campaigns in completing the Pantheon (see Plates II, VIII, and X, as well as Chapters Ten, Eleven, and Twelve). The ancient materials from the attic have been lost, save for some pieces that ended up in museums and antiquarian collections.29
Construction and Proportion
Perhaps nothing about the Pantheon is so much studied and yet so inscrutable as its structure and construction, especially that of the dome. Brick facing was used to contain the concrete, and relieving arches (arches over voids) enabled the thickness of the walls to be honeycombed with cavities that made the structure lighter and hastened the curing of the concrete (see Plate IV). The honeycombing of the rotunda’s walls extends into the zone of the springing, where the vault begins to curve inward, and up to the stepped rings at the base of the dome on the exterior. Investigations associated with conservation works have also been able to determine that the aggregate materials used in the concrete of the rotunda and dome are graded into at least six different strata, from the travertine-laden concrete at floor level to a mixture using light volcanic scoria (like pumice but denser) at the top toward the oculus (Fig. 1.12).30
1.12. Section showing gradations of heavy-to-light concrete from bottom to top. (Lancaster 2009, Fig. 8)
On the other hand, we cannot assume that the relieving arches extend as solid brick throughout the full thickness of the drum, as frequently shown in modern reconstructions. It seems more likely that in the guts of the structure, bricks are toothed to bond with the concrete (Fig. 1.13; see Chapter Five by Gene Waddell). Similarly, the foundations of the rotunda have yet to be adequately investigated, and so we remain unsure of the extent to which ground settlement might have contributed to some of the vertical cracks that punctuate the structure. The original decoration of the coffering of the dome is likewise a matter of conjecture: Did the coffers contain stellar or floral motifs? Were they elaborated with ornamental moldings? Were they painted or gilded? Was there once a system of stone or stucco facing the exterior of the rotunda, perhaps incorporating pilasters? The projections of artists and experts from the Renaissance onward may provide plausible answers, but none can be indisputably legitimized by literary, pictorial, or archaeological evidence.
1.13. Cutaway of the Pantheon showing its construction. (Conception Mark Wilson Jones, realization Robert Grover)
One of the most intellectually compelling aspects of the Pantheon is the simple proportional scheme that underlies its form. The interior diameter of the rotunda is equal in dimension to the height of the interior from pavement to oculus, while the cornice marking the division between wall and dome exactly bisects this height (see Plate XII). A hemisphere, therefore, hovers over a cylinder of the same radius and the same height, which means that a sphere can be inscribed in the whole space. Furthermore, if a square is inscribed in the circular plan of the rotunda and is then replicated (or “flipped”) to the north (Fig. 1.5), it will define the limits of the portico. Since the height of the intermediate block is the same dimension as the si
des of this square, these parts of the project together compose a cube. Thus, simple relationships govern the volumes of sphere, hemisphere, cylinder, and a cube that can be imposed on the Pantheon in the mind’s eye. These relationships suggest both a generative and a visual function for the measurements employed. In other words, the composition of the building is governed by a coherent set of dimensions, which facilitated its design and execution, as well as contributing to its essential formal aspect. Further analysis reveals how simple ratios, above all 1:1 and 1:2, resonate also in the relationships between various smaller parts of the composition (see Plate X). This, then, is a scheme of elemental beauty and simplicity redolent of Greek mathematics, a connection that Giangiacomo Martines proposes here. Indeed, the fact that the circle defining the centers of the rotunda columns has a diameter of 150 Roman feet, or 100 cubits, naturally invites speculation on a design method rooted in philosophical intent.31
Such correspondences continue to inspire theories to explain both the genesis of the design and its intentions, theories that presume the agency of a thoroughly trained and competent ancient architect. One of his skills was the ability to construct accurate technical drawings to scale. On the basis of numerous extant examples, such as a marble plan of the Temple of Castor and Pollux near the Circus Flaminius (which includes details like column bases and steps), it is clear that Roman architects used scaled plans and models, a common scale being 1:240, or 1 inch to 20 feet.32 The architect of the Pantheon may perhaps have used diagrams at this and other scales, such as 1:120 and 1:24, for the purpose of composing plans, elevations, and details. At a later stage in design, relevant information from such drawings, augmented by dimensional and proportional calculations, would have been used to construct full-scale templates, such as the set located near the entrance to the Mausoleum of Augustus, of which some, as mentioned, happen to relate to the Pantheon itself.
The Architect of the Pantheon
Unlike the Parthenon in Athens, Amiens Cathedral, St. Peter’s in Rome, Hagia Sophia, or the Taj Mahal, for the Pantheon we have no name for the architect(s) responsible. In the period under scrutiny, however, one name stands out from the prevailing anonymity, the architect-engineer Apollodorus of Damascus. Ancient sources allude to him as Trajan’s preferred designer and the author of three major projects in Rome: Trajan’s Forum, an unidentified odeon, and a gymnasium that can be presumed to be Trajan’s Baths.33 The attribution of the Pantheon to him cannot be proven, but it makes sense in several ways. He was a master architect-engineer with extensive expertise in constructing timber structures of a kind needed to provide initial support for the concrete dome. Moreover, the marble decoration in the Pantheon shares several stylistic traits with that of Trajan’s Forum by Apollodorus, including the handling of the Corinthian capitals and the disposition of the polychrome floor pattern.34 The open-air half rotundas of Trajan’s Baths also offer several points of similarity. The coffering of an exedra presents the closest-known parallel for the coffering of the Pantheon dome (see Fig. 5.7)
It is also significant that the elevations of the exedras of Trajan’s Baths present a rhythmic “syncopation” kindred to that of the interior elevation of the Pantheon, where the contrasting treatments of the three main zones (main order, attic, and dome) align only on the axes but not otherwise (see Fig. 5.3). Quite possibly this sophisticated type of treatment was a hallmark of Apollodorus or architects in his circle. Finally, with the inception date of the monument in question once more, the possibility of a Trajanic start gives added strength to the association with Apollodorus, for we know Trajan to have been his appreciative patron and supporter. By contrast, the well-known disagreements between Hadrian and his inherited architect Apollodorus, which according to one tradition proved literally fatal for the latter, would have arisen after Hadrian’s accession to power.35
The Pantheon in the Middle Ages and the Renaissance
That the Pantheon still stood in impressive condition in late antiquity is well attested in the fourth century BC by the Roman historian Ammianus Marcellinus. It was he who left that felicitous image of the rotunda resembling a city, thus calling attention to the articulation of the interior in a mode that evoked the character of urban facades. Hyperbole may have entered into his writing, yet the Pantheon must have been an extraordinarily captivating building, even by the grandiose standards of Imperial Rome. This fact more than any other must have inspired Pope Boniface IV to ask the Byzantine emperor Phocas in Constantinople to cede the “temple” to the Church in the early seventh century. Phocas ruled from 602 to 610 and Boniface IV from 608 to 615. The date usually cited for the donation is 609, but a recent analysis suggests that the event took place on May 13, 613, after the death of Phocas (see Chapter Eight by Erik Thunø).36 This would suggest that the “conversion” of the building should be contextualized in the politics of the Byzantine-dominated papacy in Rome, and not in those of the deceased Byzantine emperor.
Richard Krautheimer dismissed as legend the oft-repeated story that Boniface IV brought 28 cartloads of unnamed martyrs’ bones here from the catacombs, as it would have had little to do with contemporary customs.37 In the mid seventh century we discover the Pantheon being called Sanctae Mariae ad martyres. At the turn of the seventh–eighth centuries, the Venerable Bede likened the dedication of the Pantheon of all the ancient gods to all the martyrs of the Church, although the English monk probably had no firmer basis than tradition for doing so.38 In the latter half of the eighth century it is referred to as Sanctae Mariae Rotundae.
The twelfth-century Roman guidebook, the Mirabilia Urbis Romae, stated that the dedication to Mary supplanted an original dedication to Cybele, the mother of all of the pagan gods. The English pilgrim John Capgrave repeated this story in the early 1450s, recounting how the ancient general Agrippa had seen a vision of Cybele and vowed a church to her and all of the gods if his campaign against the Persians was successful.39 None of these dedications – not even the Christian function of the building – guaranteed it immunity from depredation. The Byzantine emperor Constans II (AD 641–668) despoiled the dome of its gilded bronze roof tiles, which were ultimately lost. Other changes to the exterior came much later. In 1270, a bell tower was constructed on the peak of the portico’s roof, and it remained in place throughout the sixteenth century, as Renaissance drawings attest.
At some unspecified moment in the medieval era, the columns on the east side of the portico were lost or severely damaged. To avoid collapse, a brick wall was erected on a portion of its front and east-facing sides. Most of the wall was eventually removed when the columns were repaired and replaced in the seventeenth century, although remnants of the brick are visible in the uppermost reaches on the east side. The elevated grade of the piazza also restricted access to the porch, reinforcing this separation between the portico and the urban space it once dominated. To descend to the ancient level of the building, three doors and side entrances were established on the perimeter of the colonnade. Their locations are indicated in sixteenth-century engravings, like Etienne Dupérac’s, and are also evident from the notches for lintels that were hacked into the porch columns, as may still be seen on site (Fig. 1.14).40 Like the date of the brick walls, that of these passages is uncertain and may be much earlier than the thirteenth-century bell tower.
1.14. Exterior view of the Pantheon; sixteenth-century engraving by Etienne Duperac. (Avery Library, Columbia University)
The state of the interior during the Middle Ages is also discussed in Chapter Eight. Thunø points out that the much-venerated image of the Madonna and Child, celebrated at the high altar and supposedly painted by St. Luke himself, can be traced no earlier than the eighth century and, thus, well after the dedication of the edifice to St. Mary and all martyrs. The high altar itself was subject to many changes. In 1270, it was marked by a ciborium composed of porphyry columns, and a low stone parapet surmounted by six more porphyry columns surrounded the altar precinct. The surrounding “pergola” must have been an
integral part of the altar complex because it was restored by Pope Innocent VIII (1484–1492), who moved it toward the center of the building in order to facilitate access to the relics of the martyrs interred under the altar. These arrangements of 1491 were complemented by a fifteenth-century maiolica relief of the Assumption of the Virgin, which hung within a painted gloria of saints in the half dome of the apse.41
In general, the Pantheon received greater respect in the Renaissance than most ancient monuments in Rome, which were often plundered for their building materials and decorative stone. Rodolfo Lanciani catalogued such acts of pillage of ancient architecture in his famous four-volume work, Storia degli scavi di Roma (1902–1912; a fifth volume appeared in 2000). The Pantheon did better than escape spoliation for the most part and was occasionally the beneficiary of these campaigns.
Under Popes Martin V (1417–1431), Eugene IV (1431–1447), Nicholas V (1447–1455), Pius II (1458–1464), and Paul II (1464–1471), efforts were devoted to shoring up the masonry of the structure, replacing or repairing the lead tiles of the dome, attending to the roof of the portico, and clearing the market stalls from the portico, the last more notable for its “squalor,” according to Flavio Biondo, than its grandeur.42 A pair of ancient Egyptian lions and a large granite urn are documented on the piazza from the later Middle Ages, and these were maintained by Eugene IV, who took the then-extraordinary step of paving the Piazza della Rotonda. Under Leo X (1513–1521), pedestals were installed under the lions and the urn to raise them above the activity of the square and preserve their integrity. Eugene’s intervention was later cited in an ordinance issued by Clement VII (1523–1534) for the maintenance of the piazza. At the beginning of the sixteenth century, their predecessor, Julius II (1503–1513), was too busy with the construction of St. Peter’s and the Vatican Palace to be interested in the Pantheon. That he left it untouched in the search for building materials for the Vatican is remarkable. Respect for the building is eloquently suggested by Raphael’s request to be buried there.