The Pantheon (temple of all the gods, in Greek) is a Roman monument built between 25 and 27 BC by the architect Marco Vipsanio Agrippa, future son-in-law of Augustus. The temple was rebuilt and remodeled by the emperor Hadrian between 118 and 125 AD and subsequently transformed into a church with the name of Santa Maria ad Martyres (609 AD).
The temple is divided into three parts: the pronaos, the avant-corps and a called "roundabout". This supports an enormous dome in which there is an enormous hole in the central part. On the entrance side we find an external colonnade of 16 columns and 4 pillars which delimit a pronaos whose space is divided into three naves. Between the pronaos and the cylindrical body we find a forepart in which there is a majestic bronze door which delimits the entrance to the temple. The door restored several times is thought to be the original one from the Hadrian era. The cylindrical part is the largest part and represents the perimeter of the internal area of the temple, the rotunda. The vault of the rotunda consists of a huge dome, in which the famous central hole called "oculus" opens. The dome is the largest in the world in non-reinforced concrete, weighing 5,000 tons and 43.44 meters in diameter. The largest and most majestic of the ancient ones.
The interior of the church has a shape which, according to Hadrian, must have represented the terrestrial globe and the celestial sphere. In the lower part of the cylindrical cell, facing the entrance, is the apse flanked by two protruding columns. On the sides, however, there are six large niches, three on each side. These niches, which house some tombs, are supported in the front by two central columns and two side pillars. In 608 AD Pope Boniface IV had the bones of many Christian martyrs kept there. Today the Pantheon preserves the tombs of the two first kings of Italy, Vittorio Emanuele II and his son Umberto I, as well as those of illustrious painters such as Annibale Carracci and the great Raphael who wanted to be buried here. Among the other tombs also that of the musician Arcangelo Corelli and the architect Baldassarre Peruzzi.
In the vault, in addition to the stupendous central hole, the coffered ceiling of the dome also attracts attention, which gradually become smaller up to the central oculus. Particular is the slightly convex floor to drain the rainwater that enters the oculus.