The Pantheon is a building of ancient Rome located in the Pigna district in the historic center, built as a temple dedicated to all past, present and future deities. It was founded in 27 a.C. dall'arpinate Marco Vipsanio Agrippa, son-in-law of Augustus. It was rebuilt by Emperor Hadrian between 120 and 124 AD, after the fires of 80 and 110 AD. they had damaged the previous construction of the Augustan age.
The building is composed of a circular structure joined to a portico in Corinthian columns that support a pediment. The large circular cell, called rotunda, is surrounded by thick masonry walls and by eight large pylons on which the weight of the characteristic hemispherical dome in concrete is distributed. The dome houses at its apex a circular opening called the oculus, which allows the illumination of the internal environment. The height of the building calculated at the oculus is equal to the diameter of the roundabout, a feature that reflects the classical criteria of balanced and harmonious architecture. Almost two millennia after its construction, the dome of the Pantheon is still today one of the largest domes in the world and specifically the largest built in unarmed concrete.
At the beginning of the seventh century the Pantheon was converted into a Christian basilica (with the edict of Constantinople) called Santa Maria della Rotonda, which allowed it to survive almost intact to the spoliazioni inflicted by the popes to the buildings of classical Rome. It enjoys the rank of minor basilica and is the only basilica in Rome as well as the patriarchal ones to still have a chapter. The inhabitants of Rome popularly called it the Rotonna, from which derive also the name of the square and street in front.