Pantheon, Rome

In the aftermath of the Battle of Actium (31 BC), Marcus Agrippa started an impressive building program: the Pantheon was a part of the complex created by him on his own property in the Campus Martius in 29–19 BC, which included three buildings aligned from south to north: the Baths of Agrippa, the Basilica of Neptune, and the Pantheon.[15] It seems likely that the Pantheon and the Basilica of Neptune were Agrippa's sacra privata, not aedes publicae (public temples).[16] The former would help explain how the building could have so easily lost its original name and purpose (Ziolkowski contends that it was originally the Temple of Mars in Campo)[17] in such a relatively short period of time.[18]

It had long been thought that the current building was built by Agrippa, with later alterations undertaken, and this was in part because of the Latin inscription on the front of the temple[19] which reads:

The Pantheon dome. The coffered dome has a central oculus as the main source of natural light.

M·AGRIPPA·L·F·COS·TERTIVM·FECIT

or in full, "M[arcus] Agrippa L[ucii] f[ilius] co[n]s[ul] tertium fecit," meaning "Marcus Agrippa, son of Lucius, made [this building] when consul for the third time."[20] However, archaeological excavations have shown that the Pantheon of Agrippa had been completely destroyed except for the façade. Lise Hetland argues that the present construction began in 114, under Trajan, four years after it was destroyed by fire for the second time (Oros. 7.12). She reexamined Herbert Bloch's 1959 paper, which is responsible for the commonly maintained Hadrianic date, and maintains that he should not have excluded all of the Trajanic-era bricks from his brick-stamp study. Her argument is particularly interesting in light of Heilmeyer's argument that, based on stylistic evidence, Apollodorus of Damascus, Trajan's architect, was the obvious architect.[21]

View of the Pantheon in Rome, including the concrete dome

The form of Agrippa's Pantheon is debated. As a result of excavations in the late 19th century, archaeologist Rodolfo Lanciani concluded that Agrippa's Pantheon was oriented so that it faced south, in contrast with the current layout that faces north, and that it had a shortened T-shaped plan with the entrance at the base of the "T". This description was widely accepted until the late 20th century. While more recent archaeological diggings have suggested that Agrippa's building might have had a circular form with a triangular porch, and it might have also faced north, much like the later rebuildings, Ziolkowski complains that their conclusions were based entirely on surmise; according to him, they did not find any new datable material, yet they attributed everything they found to the Agrippan phase, failing to account for the fact that Domitian, known for his enthusiasm for building and known to have restored the Pantheon after 80 AD, might well have been responsible for everything they found. Ziolkowski argues that Lanciani's initial assessment is still supported by all of the finds to date, including theirs; he expresses scepticism because the building they describe, "a single building composed of a huge pronaos and a circular cella of the same diameter, linked by a relatively narrow and very short passage (much thinner than the current intermediate block), has no known parallels in classical architecture and would go against everything we know of Roman design principles in general and of Augustan architecture in particular."[22]

The only passages referring to the decoration of the Agrippan Pantheon written by an eyewitness are in Pliny the Elder's Natural History. From him we know that "the capitals, too, of the pillars, which were placed by M. Agrippa in the Pantheon, are made of Syracusan bronze",[23] that "the Pantheon of Agrippa has been decorated by Diogenes of Athens, and the Caryatides, by him, which form the columns of that temple, are looked upon as masterpieces of excellence: the same, too, with the statues that are placed upon the roof,"[24] and that one of Cleopatra's pearls was cut in half so that each half "might serve as pendants for the ears of Venus, in the Pantheon at Rome".[25]

The Augustan Pantheon was destroyed along with other buildings in a fire in 80 AD. Domitian rebuilt the Pantheon, which was burnt again in 110 AD.[26]

The degree to which the decorative scheme should be credited to Hadrian's architects is uncertain. Finished by Hadrian but not claimed as one of his works, it used the text of the original inscription on the new façade (a common practice in Hadrian's rebuilding projects all over Rome; the only building on which Hadrian put his own name was the Temple to the Deified Trajan).[27] How the building was actually used is not known. The Historia Augusta says that Hadrian dedicated the Pantheon (among other buildings) in the name of the original builder (Hadr. 19.10), but the current inscription could not be a copy of the original; it provides no information as to who Agrippa's foundation was dedicated to, and, in Ziolkowski's opinion, it was highly unlikely that in 25 BC Agrippa would have presented himself as "consul tertium." On coins, the same words, "M. Agrippa L.f cos. tertium", were the ones used to refer to him after his death; consul tertium serving as "a sort of posthumous cognomen ex virtute, a remembrance of the fact that, of all the men of his generation apart from Augustus himself, he was the only one to hold the consulship thrice."[28] Whatever the cause of the alteration of the inscription might have been, the new inscription reflects the fact that there was a change in the building's purpose.[29]

Cassius Dio, a Graeco-Roman senator, consul and author of a comprehensive History of Rome, writing approximately 75 years after the Pantheon's reconstruction, mistakenly attributed the domed building to Agrippa rather than Hadrian. Dio appears to be the only near-contemporaneous writer to mention the Pantheon. Even by 200, there was uncertainty about the origin of the building and its purpose:

Agrippa finished the construction of the building called the Pantheon. It has this name, perhaps because it received among the images which decorated it the statues of many gods, including Mars and Venus; but my own opinion of the name is that, because of its vaulted roof, it resembles the heavens.

— Cassius Dio History of Rome 53.27.2

In 202, the building was repaired by the joint emperors Septimius Severus and his son Caracalla (fully Marcus Aurelius Antoninus), for which there is another, smaller inscription on the architrave of the façade, under the aforementioned larger text.[30][31] This now-barely legible inscription reads:

IMP · CAES · L · SEPTIMIVS · SEVERVS · PIVS · PERTINAX · ARABICVS · ADIABENICVS · PARTHICVS · MAXIMVS · PONTIF · MAX · TRIB · POTEST · X · IMP · XI · COS · III · P · P · PROCOS  ET

IMP · CAES · M · AVRELIVS · ANTONINVS · PIVS · FELIX · AVG · TRIB · POTEST · V · COS · PROCOS · PANTHEVM · VETVSTATE · CORRVPTVM · CVM · OMNI · CVLTV · RESTITVERVNT

In English, this means:

Emp[eror] Caes[ar] L[ucius] Septimius Severus Pius Pertinax, victorious in Arabia, victor of Adiabene, the greatest victor in Parthia, Pontif[ex] Max[imus], 10 times tribune, 11 times proclaimed emperor, three times consul, P[ater] P[atriae], proconsul, and

Emp[eror] Caes[ar] M[arcus] Aurelius Antoninus Pius Felix Aug[ustus], five times tribune, consul, proconsul, have carefully restored the Pantheon ruined by age.[32]

An 1836 view of the Pantheon by Jakob Alt, showing twin bell towers, in place from early 17th to late 19th centuries

In 609, the Byzantine emperor Phocas gave the building to Pope Boniface IV, who converted it into a Christian church and consecrated it to St. Mary and the Martyrs on 13 May 609: "Another Pope, Boniface, asked the same [Emperor Phocas, in Constantinople] to order that in the old temple called the Pantheon, after the pagan filth was removed, a church should be made, to the holy virgin Mary and all the martyrs, so that the commemoration of the saints would take place henceforth where not gods but demons were formerly worshipped."[33] Twenty-eight cartloads of holy relics of martyrs were said to have been removed from the catacombs and placed in a porphyry basin beneath the high altar.[34] On its consecration, Boniface placed an icon of the Mother of God as 'Panagia Hodegetria' (All Holy Directress) within the new sanctuary.[35]

The building's consecration as a church saved it from the abandonment, destruction, and the worst of the spoliation that befell the majority of ancient Rome's buildings during the early medieval period. However, Paul the Deacon records the spoliation of the building by the Emperor Constans II, who visited Rome in July 663:

Remaining at Rome twelve days he pulled down everything that in ancient times had been made of metal for the ornament of the city, to such an extent that he even stripped off the roof of the church [of the blessed Mary], which at one time was called the Pantheon, and had been founded in honour of all the gods and was now by the consent of the former rulers the place of all the martyrs; and he took away from there the bronze tiles and sent them with all the other ornaments to Constantinople.

Much fine external marble has been removed over the centuries – for example, capitals from some of the pilasters are in the British Museum.[36] Two columns were swallowed up in the medieval buildings that abutted the Pantheon on the east and were lost. In the early 17th century, Urban VIII Barberini tore away the bronze ceiling of the portico, and replaced the medieval campanile with the famous twin towers (often wrongly attributed to Bernini[37]) called "the ass's ears",[38] which were not removed until the late 19th century.[39] The only other loss has been the external sculptures, which adorned the pediment above Agrippa's inscription. The marble interior has largely survived, although with extensive restoration.

The interior of the Pantheon in the 18th century, painted by Giovanni Paolo Panini[40]

Since the Renaissance the Pantheon has been the site of several important burials. Among those buried there are the painters Raphael and Annibale Carracci, the composer Arcangelo Corelli, and the architect Baldassare Peruzzi. In the 15th century, the Pantheon was adorned with paintings: the best-known is the Annunciation by Melozzo da Forlì. Filippo Brunelleschi, among other architects, looked to the Pantheon as inspiration for their works.

Pope Urban VIII (1623 to 1644) ordered the bronze ceiling of the Pantheon's portico melted down. Most of the bronze was used to make bombards for the fortification of Castel Sant'Angelo, with the rest used by the Apostolic Camera for other works. It is also said that the bronze was used by Bernini in creating his famous baldachin above the high altar of St. Peter's Basilica, but, according to at least one expert, the Pope's accounts state that about 90% of the bronze was used for the cannon, and that the bronze for the baldachin came from Venice.[41] Concerning this, an anonymous contemporary Roman satirist quipped in a pasquinade (a publicly posted poem) that quod non fecerunt barbari fecerunt Barberini ("What the barbarians did not do the Barberinis [Urban VIII's family name] did").

In 1747, the broad frieze below the dome with its false windows was "restored," but bore little resemblance to the original. In the early decades of the 20th century, a piece of the original, as could be reconstructed from Renaissance drawings and paintings, was recreated in one of the panels.

Two kings of Italy are buried in the Pantheon: Vittorio Emanuele II and Umberto I, as well as Umberto's Queen, Margherita. It was supposed to be the final resting place for the Monarchs of Italy of House of Savoy, but the Monarchy was abolished in 1946 and the authorities have refused to grant burial to the former kings who died in exile (Victor Emmanuel III and Umberto II). The National Institute for the Honour Guard of the Royal Tombs of the Pantheon, which mounts guards of honour at the royal tombs of the Pantheon, was originally chartered by the House of Savoy and subsequently operating with authorization of the Italian Republic, mounts as guards of honour in front of the royal tombs.

The Pantheon is in use as a Catholic church, and as such, visitors are asked to keep an appropriate level of deference. Masses are celebrated there on Sundays and holy days of obligation. Weddings are also held there from time to time.

The portico

The building was originally approached by a flight of steps. Later construction raised the level of the ground leading to the portico, eliminating these steps.[5]

The pediment was decorated with relief sculpture, probably of gilded bronze. Holes marking the location of clamps that held the sculpture suggest that its design was likely an eagle within a wreath; ribbons extended from the wreath into the corners of the pediment.[42]

On the intermediate block between the portico and the rotunda, the remains of a second pediment suggests that the existing portico is much shorter than originally intended. A portico aligned with the second pediment would fit columns with shafts 50 Roman feet (14.8 metres) tall and capitals 10 Roman feet tall (3 metres), whereas the existing portico has shafts 40 Roman feet (11.9 metres) tall and capitals eight Roman feet (2.4 metres) tall.[43][44]

Mark Wilson Jones has attempted to explain the design adjustments by suggesting that, once the higher pediment had been constructed, the required 50-foot columns failed to arrive (possibly as a result of logistical difficulties).[43] The builders then had to make some awkward adjustments to fit the shorter columns and pediments. Rabun Taylor has noted that, even if the taller columns were delivered, basic construction constraints may have prevented their use.[44] Assuming that each column would first be laid on the floor next to its pediment before being pivoted upright (using something like an A-frame), there would be a space requirement of a column-length on one side of the pediment, and at least a column-length on the opposite side for the pivoting equipment and ropes. With 50 foot columns, "there was no way to sequence the erection of [the columns] without creating a hopeless snarl. The shafts were simply too long to be positioned on the floor in a workable configuration, regardless of sequence."[44] Specifically, the innermost row of columns would be blocked by the main body of the temple, and in the later stages of construction some already-erected columns would inevitably obstruct the erection of further columns.

It has also been argued that the scale of the portico was related to the urban design of the space in front of the temple.[45]

The grey granite columns that were used in the Pantheon's pronaos were quarried in Egypt at Mons Claudianus in the eastern mountains. Each was 11.9 metres (39 ft) tall, 1.5 metres (4 ft 11 in) in diameter, and 60 tonnes (59 long tons; 66 short tons) in weight.[46] These were dragged more than 100 km (62 miles) from the quarry to the river on wooden sledges. They were floated by barge down the Nile when the water level was high during the spring floods, and then transferred to vessels to cross the Mediterranean Sea to the Roman port of Ostia. There, they were transferred back onto barges and pulled up the Tiber River to Rome.[47] After being unloaded near the Mausoleum of Augustus, the site of the Pantheon was still about 700 metres away.[48] Thus, it was necessary to either drag them or to move them on rollers to the construction site.

In the walls at the back of the Pantheon's portico are two huge niches, perhaps intended for statues of Augustus Caesar and Agrippa.

The large bronze doors to the cella, measuring 4.45 metres (14.6 ft) wide by 7.53 metres (24.7 ft) high, are the oldest in Rome.[49] These were thought to be a 15th-century replacement for the original, mainly because they were deemed by contemporary architects to be too small for the door frames.[50] Later analysis of the fusion technique confirmed that these are the original Roman doors,[49] a rare example of Roman monumental bronze surviving, despite cleaning and the application of Christian motifs over the centuries.

Cross-section of the Pantheon showing how a 43.3-metre diameter sphere fits under its dome.

The 4,535-tonne (4,463-long-ton; 4,999-short-ton) weight of the Roman concrete dome is concentrated on a ring of voussoirs 9.1 metres (30 ft) in diameter that form the oculus, while the downward thrust of the dome is carried by eight barrel vaults in the 6.4-metre-thick (21 ft) drum wall into eight piers. The thickness of the dome varies from 6.4 metres (21 ft) at the base of the dome to 1.2 metres (3.9 ft) around the oculus.[51] The materials used in the concrete of the dome also vary. At its thickest point, the aggregate is travertine, then terracotta tiles, then at the very top, tufa and pumice, both porous light stones. At the very top, where the dome would be at its weakest and vulnerable to collapse, the oculus lightens the load.[52]

Beam in the dome of the Pantheon

No tensile test results are available on the concrete used in the Pantheon; however, Cowan discussed tests on ancient concrete from Roman ruins in Libya, which gave a compressive strength of 20 MPa (2,900 psi). An empirical relationship gives a tensile strength of 1.47 MPa (213 psi) for this specimen.[51] Finite element analysis of the structure by Mark and Hutchison[53] found a maximum tensile stress of only 0.128 MPa (18.5 psi) at the point where the dome joins the raised outer wall.[3]

The stresses in the dome were found to be substantially reduced by the use of successively less dense aggregate stones, such as small pots or pieces of pumice, in higher layers of the dome. Mark and Hutchison estimated that, if normal weight concrete had been used throughout, the stresses in the arch would have been some 80% greater. Hidden chambers engineered within the rotunda form a sophisticated structural system.[54] This reduced the weight of the roof, as did the oculus eliminating the apex.[55]

The top of the rotunda wall features a series of brick relieving arches, visible on the outside and built into the mass of the brickwork. The Pantheon is full of such devices – for example, there are relieving arches over the recesses inside – but all these arches were hidden by marble facing on the interior and possibly by stone revetment or stucco on the exterior.

The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142 ft), so the whole interior would fit exactly within a cube (or, a 43.3-m sphere could fit within the interior).[56] These dimensions make more sense when expressed in ancient Roman units of measurement: The dome spans 150 Roman feet; the oculus is 30 Roman feet in diameter; the doorway is 40 Roman feet high.[57] The Pantheon still holds the record for the world's largest unreinforced concrete dome. It is also substantially larger than earlier domes.[58] It is the only masonry dome to not require reinforcement. All other extant ancient domes were either designed with tie-rods, chains and banding or have been retrofitted with such devices to prevent collapse.[59]

Though often drawn as a free-standing building, there was a building at its rear which abutted it. While this building helped buttress the rotunda, there was no interior passage from one to the other.[60]

External video
The Pantheon, Rome, (8:31) Smarthistory

Upon entry, visitors are greeted by an enormous rounded room covered by the dome. The oculus at the top of the dome was never covered, allowing rainfall through the ceiling and onto the floor. Because of this, the interior floor is equipped with drains and has been built with an incline of about 30 centimetres (12 in) to promote water runoff.[61][62]

The interior of the dome was possibly intended to symbolize the arched vault of the heavens.[56] The oculus at the dome's apex and the entry door are the only natural sources of light in the interior. Throughout the day, light from the oculus moves around this space in a reverse sundial effect: marking time with light rather than shadow.[63] The oculus also offers cooling and ventilation; during storms, a drainage system below the floor handles rain falling through the oculus.

The dome features sunken panels (coffers), in five rings of 28. This evenly spaced layout was difficult to achieve and, it is presumed, had symbolic meaning, either numerical, geometric, or lunar.[64][65] In antiquity, the coffers may have contained bronze rosettes symbolising the starry firmament.[66]

Circles and squares form the unifying theme of the interior design. The checkerboard floor pattern contrasts with the concentric circles of square coffers in the dome. Each zone of the interior, from floor to ceiling, is subdivided according to a different scheme. As a result, the interior decorative zones do not line up. The overall effect is immediate viewer orientation according to the major axis of the building, even though the cylindrical space topped by a hemispherical dome is inherently ambiguous. This discordance has not always been appreciated, and the attic level was redone according to Neoclassical taste in the 18th century.[67]