The Pantheon is the building of ancient Rome which has been preserved best down to the present day, and is a true masterpiece of architecture. The name of Agrippa, which can still be read on the facade, remembers the son-in-law of the Emperor Augustus, who first built this temple dedicated "to all the gods". The present-day Pantheon, however, completely different from the original, is the work of the Emperor Hadrian, who rebuilt the monument in the early 2nd century, keeping only the ancient inscription out of modesty.

In the 6th century the Byzantine emperor Phocas gave the building to Pope Boniface IV, who turned it into the present church of Sancta Maria ad Martyres.

For the solemn consecration of the church, the pope had 28 cartloads of bones of martyrs brought from the catacombe, putting them underneath the altar. During the ceremony, as the notes of the Gloria were struck, the Romans saw swarms of devils rise up and fly out the hole in the dome.

The most amazing characteristic of the building is the exceptional covering dome. lt is the largest dome ever created out of concrete: it measures 43.30 mt. in diameter and is greater than that of the dome of St.Peter's!

The entire building is conceived as a perfect geometric figure: a sphere inserted in a cylinder. The diameter of the sphere coincides with height of the cylinder. The dome, created with different materials, increasingly lighter as they go upwards, ends with a large open "eye"', of a diameter of 9 metres. Through this opening enters the rain, which is conveyed into the drains visibie on the pavement.