The Pantheon is one of the most iconic buildings in Rome, Italy. It was commissioned by Marcus Agrippa at the time of the reign of Emperor Augustus (27 BC – 14 AD) and rebuilt by Emperor Hadrian in around 126 AD.
The building is circular with a portico of large stone Corinthian columns (eight make up the front group and two sets of four behind) under a pediment. A rectangular vestibule links the porch to the rotunda, which is under a coffered concrete dome, with a central opening (oculus) to the sky. Almost two thousand years after it was built, the Pantheon’s dome is still the world’s largest unreinforced concrete dome. The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142 ft).
It is one of the best-preserved of all Ancient Roman buildings. It has been in continuous use throughout its history, and since the 7th century, the Pantheon has been used as a church dedicated to “St. Mary and the Martyrs” but informally known as “Santa Maria Rotonda”. The square in front of the Pantheon is called Piazza della Rotonda.
RotundaThe 4,500 (plus) metric tons weight of the Roman concrete dome is concentrated on a ring of voussoirs 9 metres, or 30 ft in diameter – forming the oculus. The downward thrust of the dome is carried by eight barrel vaults in the 6.4 metres (21 ft) thick 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.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. Finite element analysis of the structure by Mark and Hutchison found a maximum tensile stress of only 128 kPa (18.5 psi) at the point where the dome joins the raised outer wall.
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 honeycomb structure. This reduced the weight of the roof, as did the elimination of the apex by means of the oculus.
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 (also, the interior could house a sphere 43.3 metres (142 ft) in diameter). 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. The Pantheon still holds the record for the world’s largest unreinforced concrete dome. It is also substantially larger than earlier domes.
Though often drawn as a free-standing building, there was a building at its rear into which it abutted. While this building helped buttress the rotunda, there was no interior passage from one to the other.
The interior of the dome was possibly intended to symbolize the arched vault of the heavens. The oculus at the dome’s apex and the entry door are the only natural sources of light in the interior. Throughout the day, the light from the oculus moves around this space in a reverse sundial effect. The oculus also serves as a cooling and ventilation method. During storms, a drainage system below the floor handles the rain that falls 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. In antiquity, the coffers may have contained bronze stars, rosettes, or other ornaments.
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.
Pantheon is derived from the Ancient Greek “Pantheion” (Πάνθειον) meaning “of, relating to, or common to all the gods”: (Pan /”Παν” meaning “all” + Theion / “θειον”= meaning “gods”). Cassius Dio, a Roman senator who wrote in Greek, speculated that the name comes either from the statues of so many gods placed around this building, or from the resemblance of the dome to the heavens. His uncertainty strongly suggests that “Pantheon” (or Pantheum) was merely a nickname, not the formal name of the building. In fact, the concept of a pantheon dedicated to all the gods is questionable. The only definite pantheon recorded earlier than Agrippa’s was at Antioch in Syria, though it is only mentioned by a sixth-century source. Ziegler tried to collect evidence of panthea, but his list consists of simple dedications “to all the gods” or “to the Twelve Gods,” which are not necessarily true panthea in the sense of a temple housing a cult that literally worships all the gods.
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. It seems likely that the Pantheon and the Basilica of Neptune were Agrippa’s sacra privata, not aedes publicae (public temples). This less solemn designation 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) in such a relatively short period of time.
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 inscription on the front of the temple which reads:
In 609, the Byzantine emperor Phocas gave the building to Pope Boniface IV, who converted it into a Christian church and consecrated it to Santa Maria ad Martyres, now known as Santa Maria dei Martiri: “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.”
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. 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. 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) called “the ass’s ears,” which were not removed until the late 19th century. 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.
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 remaining amount used by the Apostolic Camera for various 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. This led the Roman satirical figure Pasquino to quip: Quod non fecerunt barbari fecerunt Barberini (“What the barbarians did not do the Barberini [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.