Pantheon, Rome

The Pantheon is a domed temple in the Campus Martius, the old Field of Mars in the centre of Rome. A first temple on the spot was raised by Marcus Agrippa in the reign of Augustus; the building that stands today was rebuilt in the early second century and completed under the emperor Hadrian. Its unreinforced concrete dome remains the largest of its kind in the world, and because it has been in use almost without a break, first as a temple and since 609 as a church, it is one of the best-preserved buildings of ancient Rome.

After the battle of Actium in 31 BCE Agrippa laid out a complex on his own land in the Campus Martius between 29 and 19 BCE, with baths, a basilica of Neptune and the Pantheon. What his temple looked like is disputed. Excavations in the late nineteenth century led the archaeologist Rodolfo Lanciani to conclude that it faced south and had a T-shaped plan, while later digs suggested a round building facing north like the present one; the scholar Ziolkowski has argued that the evidence still favours Lanciani. Pliny the Elder recorded that the temple had capitals of Syracusan bronze and caryatid columns by Diogenes of Athens.

Agrippa's temple burned in 80 CE, and Domitian's restoration burned again in 110. The present building is usually dated to Hadrian's reign and is thought to have been dedicated around 126, though the date is uncertain because Hadrian put Agrippa's original inscription back on the new porch. Some scholars, such as Lise Hetland, argue that work began in 114 under Trajan, and Trajan's architect Apollodorus of Damascus has been proposed as its designer. The emperors Septimius Severus and Caracalla repaired it in 202, as a smaller inscription records. How the temple was used in antiquity is not known.

A columned porch with a triangular pediment leads through a rectangular block into a round hall roofed by a coffered concrete dome. The height to the opening at the top, the oculus, equals the diameter of the interior, about 43 metres, so that a sphere would fit exactly inside; in Roman units the dome spans 150 feet. The builders used lighter materials, ending with pumice and tufa, as the dome rose, and the open oculus removed weight from its weakest point.

In 609 Phocas, emperor of the Byzantine Empire, handed the building over to Pope Boniface IV, who consecrated it on 13 May as a church of Saint Mary and the Martyrs, reputedly with many cartloads of martyrs' relics brought from the catacombs. This conversion spared it from the abandonment and plunder suffered by most of Rome's ancient buildings, though not entirely: in 663 the emperor Constans II, visiting from Constantinople, took its bronze roof tiles, and the dome stayed uncovered until Gregory III had it roofed in lead in the 730s. Over the Middle Ages the marble facing and pediment sculpture disappeared, a belfry was added in 1270, and stalls crowded the porch. In the fifteenth century the popes repaired the roof and cleared the square.

From the Renaissance the church became a burial place for artists, including the painter Raphael and the composer Arcangelo Corelli. Pope Urban VIII stripped the bronze beams of the porch in the 1620s and 1630s, mostly to cast cannon for Castel Sant'Angelo, prompting the Latin jibe that what the barbarians had spared the Barberini had done. He also added twin bell towers, mocked as "the ass's ears". A Neoclassical remodelling of the attic in the 1750s was widely criticised, and part of the original design was restored in the 1930s.

After the unification of Italy, two kings, Victor Emmanuel II and Umberto I, were buried in the Pantheon. The bell towers came down in 1883, restoration of the dome and brickwork began in 1928, and further repairs to the roof and dome took place in 2004 and 2005. The building is state property and remains a working Catholic church.