The Pantheon

The story

The temple of all the gods

Walk into the Pantheon and look up. Above you is an enormous dome, with no columns or supports, and right at the top an open circle through which the light of the sky comes in. It is one of the best-preserved ancient buildings in the world. Its name comes from Greek and means “of all the gods”.

The Pantheon we see today is not the first. A first temple was built around 27–25 BC by Marcus Vipsanius Agrippa, friend and son-in-law of Augustus, in the Campus Martius, the part of Rome where many public monuments stood. It was very different: it had a rectangular plan, measured about 44 metres by 20, was built of travertine and faced with marble. That temple burned down in AD 80, was restored under the emperor Domitian and destroyed again, after a lightning strike, around 110, under Trajan.

A building site of many years

The rebuilding of the present building took place under Trajan and Hadrian. Scholars do not agree on the dates: the reconstruction must have taken a period between about 112 and 128, and the dedication of the temple may have been made between 125 and 127. Many scholars think that the work began under Trajan, around 114, and was finished by Hadrian: this is suggested by the brick stamps, that is, the maker's marks pressed into the bricks, which date mostly from the last years of Trajan and the first of Hadrian. For this reason the date is approximate, around 125.

On the façade, however, Hadrian did not put his own name. You can still read today Agrippa's inscription, carried over onto the new building: M·AGRIPPA·L·F·COS·TERTIVM·FECIT, that is, “Marcus Agrippa, son of Lucius, consul for the third time, built it”. It is a way of respecting the past.

Outside: the portico

The entrance is a great portico, the pronaos, with 16 Corinthian columns. Eight are of grey granite, quarried at Mons Claudianus, and eight of pink granite, quarried at Aswan, both in Egypt. Think what an effort it was to carry enormous columns from Egypt to Rome. The entrance door is of bronze, 4.45 metres wide and 7.53 high: it is considered the oldest and most imposing bronze door still in use in Rome.

Inside: the rotunda

Beyond the portico opens the great circular hall, the rotunda. The cylinder of the walls is 21.72 metres high, which is the same as the radius of the hall. The dome has a diameter of about 43.4 metres, and its interior height is equal to the diameter. This means that a sphere would fit perfectly inside the hall. For centuries it was the largest dome in the world, and even today it is the largest ever built in unreinforced concrete, that is, without iron bars inside.

The dome is decorated with five rows of coffers, that is, sunken panels, 28 in each row, getting smaller as they go up. The number 28 was considered perfect by the ancients. The coffers are not only beautiful: they lighten the weight.

The secret lies in the material. The concrete is not the same everywhere: at the bottom it is heavier, with pieces of travertine and tuff; as you go up it becomes lighter, with pumice and volcanic lapilli. The thickness of the shell decreases from about 6 metres at the base to a little over a metre near the top. In this way the overall weight is less and the dome does not collapse.

At the top is the oculus, a large circular opening. It is the only source of light in the building, apart from the door. The smooth band surrounding it measures about 9 metres across.

From temple to church

The Pantheon has been preserved almost intact because it was never abandoned. In 608 the Eastern emperor Phocas gave it to Pope Boniface IV, who in 609 turned it into a church, dedicated to St Mary and the Martyrs, the Sancta Maria ad Martyres. Today it is still a church. Inside lie the painter Raphael, the painter Annibale Carracci, the kings of Italy Victor Emmanuel II and Umberto I, and Queen Margherita.