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This much can be said with certainty: with its north-facing orientation, Agrippa’s Pantheon was aligned axially with the entrance to the Mausoleum of Augustus about half a mile away, a critical relationship that encourages its interpretation as a dynastic sanctuary (see Plate XVI). This pairing accords with a passage by Dio Cassius, a consul of the third century, which states that Agrippa intended to honor the emperor by dedicating the building to him and erecting his statue inside, but Augustus disapproved. Agrippa therefore placed a statue of the deified Julius Caesar (Augustus’s adoptive father) in the building along with those of the Olympian gods, including Venus and Mars, whereas statues of himself and Augustus were set up in the porch, presumably in the two great niches. As La Rocca’s chapter argues, Dio’s remark and other evidence show that the Pantheon had a special place in a sophisticated program celebrating Augustus and anticipating his future divinization. None of the statues has survived, nor do we have later notice of them. It is safe, though, to assume that Venus, Mars, and Julius Caesar were accompanied by other statues disposed in the exedras and aedicules of the rotunda. It is also likely that the statues of divinized members of the imperial family were added to the original deities from time to time, as the initial dynastic aspect of the program evolved into a celebration of the imperial institution and its divine authority.
Agrippa’s Pantheon was damaged by fire in AD 80, restored to some unknown extent by the emperor Domitian (AD 51–96), struck by lightning and burned again in AD 110, before being rebuilt in its present form and completed around AD 125–128 during the reign of Hadrian (AD 117–138). This building was then refurbished in AD 202 under Septimius Severus (AD 193–211) and Caracalla (AD 211–217), as is indicated in an inscription on the facade carved in small letters under the Agrippan inscription.
Given the inscription’s prominence, Agrippa’s patronage of the present building was generally accepted until 1891–1892, when excavations revealed traces of an earlier building under the porch and a polychrome marble pavement under the rotunda. The impetus for these excavations came from the work of a young French architect, Georges Chédanne, a pensionnaire at the French Academy in Rome, who overturned prevailing assumptions by assigning the Pantheon to Hadrian’s reign on the basis of brickstamps belonging to the structure.10 (Roman brickmakers often stamped one brick per batch with information that in effect yields a date range and sometimes the precise year of manufacture.) This drastic revision resituated the building firmly in the period of the Roman Empire during a time of great architectural innovation in the use of the very sort of concrete technology that the Pantheon exemplified. The inscription below the pediment was newly understood as a gesture of respect recalling the earlier Agrippan fabric, thus commemorating the original builder as Hadrian supposedly did in other rebuilding or restoration projects. Chédanne’s conclusions met with a sympathetic echo at the time in the research of Heinrich Dressel, the first systematic scholar of brickstamp evidence, and they were confirmed in the major modern study of brickstamps by Herbert Bloch in 1948.11
Lately, a new interpretation has emerged, questioning the data and proposing that many of the bricks from the Pantheon previously thought to be Hadrianic are in truth datable to the end of the reign of Trajan (98–117). Indeed, on the basis of a rigorous reappraisal of the facts, presented in this volume by Lise Hetland and already the subject of scholarly excitement, it now seems that just one of the 90 stamps from the monument catalogued by Bloch can be dated to Hadrian’s reign with absolute confidence. Thus, we face some forceful evidence for attributing the planning and inception of the Pantheon earlier, to Trajan’s reign, with only its completion owed to his successor Hadrian.
The Porch
As Rome declined and the city shrank from the boundaries of its ancient walls after the fourth century AD, the decay and collapse of buildings, the repeated flooding of the Tiber, and the demise of drainage systems produced an inexorable rise of the ground level. As a result, instead of standing proud of its surroundings as it once did, the Pantheon now lies somewhat depressed in the urban tissue. Excavations carried out in the Piazza della Rotonda in front of the porch in 1997–1998 revealed the ancient pavement level lying some two meters below the modern level.12 The disparity between the ancient and modern pavement levels was, as we shall see, even more pronounced in the Renaissance, when visitors had to descend about seven steps from the surrounding ground level to reach the floor of the portico (Fig. 1.4).
1.4. View of portico interior; drawing by Maarten van Heemskerck, ca. 1532–1536. (Berlin, Kupferstichkabinett, Roman sketchbooks, vol. 2, fol. 2 recto)
The eight columns that define the facade of the Pantheon stand in front of eight more columns arranged so as to form two aisles and a central passage. The total of 16 columns, together with the four square antae that mediate between the portico and the transitional block, support an entablature and a tile-covered roof that is fronted by the imposing pediment.13 All stonework divides into two kinds: near-white marble from the quarries on Mount Pentelicon near Athens (the same marble that was used to make the Parthenon and its sculptures) and granite from Egypt. The granite came, in turn, from two quarries, the rose or pink granite from Aswan and the gray granite from the more remote quarry at Mons Claudianus, located between the Red Sea and the Nile. The eight columns of the front have shafts of the gray hue, while the other eight have shafts of pink, though due to patination and grime, the chromatic variation can seem marginal in some light conditions. In both cases, the shafts are each of a single piece (save for a few repairs), that is to say, monoliths weighing 50 tons. The pediment carried by the columns and the entablature with the inscriptions no doubt displayed a symbolically charged decoration in bronze, as implied by the presence of numerous fixing holes. Their pattern has led to the inspired yet unprovable reconstruction of a civic honor in the shape of a crown of oak leaves (corona civica), combined perhaps with an eagle alluding to the apotheosis of mortals to the immortal realm.14
The roof over the portico runs back to interrupt a secondary pediment applied to the surface of the transitional block, creating a compositional oddity that inspired the invention of a new kind of church facade in the sixteenth century. This unusual configuration, together with certain anomalous characteristics in different parts of the portico, especially the unhappy resolution of its meeting with the rotunda at the transitional block, represents a long-standing source of puzzlement. A controversial recent theory, advocated here on the basis of fresh corroborative evidence in Chapter Seven, proposes that the initial plan called for columns of even greater size, each weighing no less than 100 tons. For some unexplained reason (possibly a disaster such as a shipwreck), the columns originally intended were lost, and construction proceeded with the smaller-size columns we see today, a change that could help to explain the various anomalies of the portico as executed.15
Analysis of the design of the portico and its geometry and proportions is rendered more complex by this theory, but either way, it is possible to observe the harmonious numerical simplicity of proportions that is an enduring hallmark of monumental Roman architecture. As built, for example, the columns conform to the conventional rhythm known as systyle, in which the space between the columns is double their diameter, whereas the originally intended rhythm would have been pycnostyle, with the space between the columns being one and a half times their diameter. The overall scheme for the portico and transitional block meanwhile is one of archetypal simplicity, with a total height that matches its width (as measured between the centers of the corner columns) (Fig. 1.5).16
1.5. Schematic geometry of the Pantheon. (Wilson Jones 2000, Fig. 9.11)
Such observations come from a scrutiny of surveyed measurements understood in the light of surviving ancient textual evidence, above all the treatise on architecture by the Roman architect and writer Vitruvius (ca. 80–70 BC–after 15 BC) that was completed not long after the building of Agrippa’s Pantheon. We also have direct physical evidence for explain
ing how the actual design of the present building was carried out, how its stones were measured, and how they were cut. This evidence, which is another recent discovery, takes the form of a set of ancient Roman profiles for the portico etched full scale into the limestone paving that lies in front of the Mausoleum of Augustus (Fig. 1.6, a and b). As Lothar Haselberger has shown, parts of these templates match the features of the Pantheon pediment so closely that we can presume they were used in the process of shaping the stone and other materials unloaded from barges at this site, which had long hosted docking facilities for commodities that moved up and down the Tiber River.17 The templates include such details as the exact column spacing of the portico according to the executed dimensions and the configuration of the bracket-like modillions punctuating the cornice. The profiles seem to forecast the use of the Corinthian capitals, although, if truth be told, the size indicated is too big with respect to those of the actual building and yet, by an uncanny coincidence, just the right measure for the original columns posited for the project.
1.6. a) West corner of pediment (Haselberger 1994, Abb. 5), and b) full-scale etching of profiles for portico elevation, limestone paving in front of Mausoleum of Augustus. (Haselberger 1994, Abb. 1)
By means of the same template, we can restore the original outline of the capitals, nearly all of which have suffered serious damage over time. Here, as is generally the case, damage to the fabric of the Pantheon has been more the result of human intervention than time or natural causes. The whole portico was colonized, mutilated, and added to repeatedly down the centuries, culminating in the disappearance of the three east columns at some as yet unknown date (Fig. 1.7). Popes Urban VIII Barberini (1623–1644) and Alexander VII Chigi (1655–1667) replaced the columns in campaigns with their own historical contexts. That of the Barberini also involved the stripping of bronze trusses from the roof of the portico and their replacement with timber, leading to the famous pasquinade, Quod non fecerunt barberi, fecerunt Barberini (“What the barbarians didn’t do, the Barberini did”). The fuller context is recounted in the following and more extensively in the chapter on the Pantheon during the seventeenth century.
1.7. Exterior view of Pantheon; anonymous sixteenth-century drawing. (Louvre inv. 11029 recto)
Suspended from the original bronze trusses there may have been great barrel-vaulted ceilings likewise made of bronze, with a larger vault for the central nave and smaller ones for the flanking aisles.18 The effect of the central vault can be visualized most easily by imagining the coffered barrel vault presently over the entrance portal extending across the vestibule as it was depicted in the sixteenth century (Fig. 1.8). The only ancient assembly of bronze that does survive at the Pantheon is the grandiose portal made of two opening leaves slung on vertical pivot hinges framed by fluted pilasters at the sides, with an open grille overhead.19 All of this fits within the 20-by-40-foot opening in the masonry, while the threshold is one of the largest single pieces of stone in the whole edifice, a slab of highly prized blood-and-black africano, 20 feet long, 5 feet wide, and of unknown depth. The fact that the door leaves do not fill the opening without the grille, along with some stylistic clues, suggests that they could have been reutilized from some earlier building. While this may not have been the Pantheon of Agrippa itself on account of the two intervening destructive fires, an allusion of continuity may nevertheless have been intended, in keeping with the restitution of Agrippa’s name in the main inscription. This notion is strengthened by the presence of candelabra, festoons, ribbons, and religious utensils carved in the friezes that run at intervals around the walls of the transitional block, as these second-century AD decorations recall comparable motifs used for the first time on Augustan monuments.20
1.8. Door and vault in portico; drawing by Raphael. (Uffizi A 164 verso)
The Intermediate Block
The link between the porch of the Pantheon and the rotunda is formed by the so-called intermediate or transitional block. These names reflect the fact that its form had to mediate between the rectilinear geometry of the portico and the circular geometry of the rotunda.21 This is the main explanation for the very existence of the intermediate block; it had no known use other than to house a pair of staircases that rise up the full height of the structure to give access to the roof. At a high level, the stairs also provide the means of entry to a group of rooms later occupied by the Accademia dei Virtuosi, an association of artists that was based here since the sixteenth century. In antiquity, these spaces were no doubt put to use, but there is nothing to tell us how that use factored into their creation.
The intermediate block is built of brick-faced concrete, whose exterior is still covered in some places by dressed stone and decorative elements (Fig. 1.9). These decorations consist of fluted pilasters and the series of friezes already mentioned that are carved in relief on three-foot-tall slabs of marble varying in length and arranged as two horizontal bands on the intermediate block, as well as three bands to either side of the entrance portal. Originally 28 in number (10 on both flanks and 8 by the entrance), each of the reliefs shows a garland slung between two candelabras, with small religious utensils represented as though hovering over the garlands in the center.22
1.9. Exterior of intermediate block, west side. (Photo Mark Wilson Jones)
The top of the intermediate block is capped by a cornice with simple S-shaped modillions that continues around the rotunda as a unifying device. However, other aspects of the composition in this area of the building undermine its unity. The superimposed outline of a pediment with raking cornices bearing similar modillions on the front (north) face of the block is cut into by the roof of the portico and rendered incomplete, as already observed. Meanwhile, the marble entablature over the columns, with its more elaborate smaller modillions, runs down the sides of the intermediate block and dead-ends unceremoniously at the rotunda without any corresponding architectural feature on the curved body of the building.
The formal distinctions between the rotunda and portico and their imperfect resolution in the intermediate block were so pronounced in the eyes of Renaissance viewers that they believed the rotunda and the porch to have been conceived at different times, with the intermediate block usually being associated either with one or the other. An evident interruption in the structural bonding of the transitional block with the rotunda supported this notion. Some informed observers dated the rotunda to the Republic and considered the portico a later addition under Agrippa. Still others thought that Agrippa must have built the rotunda during the reign of Augustus, while the portico should be attributed to later emperors, either Hadrian or Antoninus Pius or Septimius Severus, for all of whom there was some epigraphic and literary testament. Yet a third camp of observers insisted that the portico was Agrippa’s and so came first, the rotunda having been somewhat clumsily added to it.23 These theories help to explain why the dating of the transitional block and indeed the entire monument has oscillated from one era to another in the eyes of different scholars.
After the 1890s, all this had to change with the arrival of the brickstamp analyses of Chédanne and Dressel, which seemed to date the whole building firmly to the reign of the emperor Hadrian.24 Momentarily leaving aside the question of the starting date, Hetland’s review of the evidence is significant in confirming that the construction of the rotunda and intermediate block were contemporary, at least at lower levels. This conclusion is clinched by a detail that escaped earlier publications of the building: the presence in the staircase of so-called bonding courses of large, double-size bricks, or bipedales, that traverse the tissue of the rotunda on one side and the intermediate block on the other (see Chapter Seven and Plate XXIII).25 Despite past interpretations, one thing is now clear: the transitional block belonged to a single project along with the rotunda and the portico.
The Rotunda and Dome
It is fair to say that most modern visitors find the expansive domed interior of the Pantheon to be its most impressive feature, and its crow
ning open oculus to be its most surprising. This gaping hole, 30 feet (about 9 meters) in diameter, admits light and air and even rain, but most importantly the ever-changing illumination created by the motion of the sun. There were precedents such as the so-called Temple of Mercury at Baiae, but the effect in the Pantheon is unrivaled as a sensory architectural experience (see Plate IX). Had the interior been built when the canonic Seven Wonders of the World were formulated, it surely would have been among their number.
The rotunda is a domed cylinder 55 meters in diameter, with an interior space nearly 44 meters wide spanned by a hemispherical dome. As was common in Roman centralized buildings, the circular geometry of the plan is articulated by two main orthogonal axes and two diagonal axes so as to create eight sectors like slices of a pie (see Plate V). The perimeter is articulated by large alcoves, or exedras, that seem as though they are carved out of the 20-foot-thick (6 meter) drum, leaving eight structural “piers” between them (see Plates IV and VI). On the cross axis, the exedras are semicircular, while on the diagonal axes their plan follows the curve of the rotunda. The main axis runs through the rectangular entrance space and terminates at the semicircular exedra that is the main apse (Fig. 1.10).
IV. Diagrams of cavities in the wall. (The Bern Digital Pantheon Project, BERN BDPP0087, drawn from information in Licht 1968)
V. Plan of pavement, niches, and high altar; anonymous seventeenth-century drawing associated with the Bernini workshop. (Biblioteca Apostolica Vaticana, Chigi P VII, 9, 108 recto)
VI. Interior view featuring pier with Raphael’s tomb and flanking niches. (The Bern Digital Pantheon Project, BERN BDPP0069)