Today a Christian church, the Pantheon is the best preserved of all ancient Roman buildings and has been in near-continuous use since Hadrian’s reconstruction. From a distance the Pantheon is not as awe-inspiring as other ancient monuments — the dome appears low, not much higher than surrounding buildings. Inside, the Pantheon is among the most impressive in existence. Its inscription, M·AGRIPPA·L·F·COS·TERTIUM·FECIT, means: Marcus Agrippa, son of Lucius, consul for the third time, built this.

"Pan" meaning everything and "theon" - divine, formed a combined symbolism as a homage to "all the Gods". The Pantheon was originally built as a pagan temple for the common people to worship the 7 Roman Gods - Sun, Moon, Venus, Saturn, Jupiter, Mercury, Mars.

The concept was quite revolutionary because before then temples were strictly for priests and vestals.

The original Roman Pantheon, which succumbed to fire in A.D. 80, was constructed in 27 - 25 B.C. by emperor Marcus Agrippa, and according to Roman mythology the Pantheon stands on the spot where Romulus was carried away by an eagle after he died.

The much larger Roman Pantheon that we see today was built by Emperor Hadrian between 118 and 125 A.D. and stands on some of the foundations of the original structure. The pediment of the portico was taken from the original Pantheon and placed there by Hadrian. The inscription, which reads "M.AGRIPPA.L.F.COS.TERTIUM.FECIT", means: "Marcus Agrippa son of Lucius consul for the 3rd time built this".

In 609 B.C. the Roman Pantheon was given to the Catholic Church by Byzantine Emperor Phocas, and subsequently consecrated by Pope Boniface IV as the Church of Santa Maria and Martyres, which is what it remains to this day. This consecration (which was seen by some to be a poaching by the Catholic Church) was not such a bad thing as it most likely saved the building from falling into disrepair, a fate suffered by many ancient Roman buildings.

It was during the reign of Pope Urban VIII (of the Barberini family) that the Roman Pantheon suffered most of its desecration. The bronze adorning, which covered the columns and ceiling of the Portico, was stripped melted and used to build canons for the Castel Sant'Angelo and also to build the Baldachin (altar) which stands above St Peter's tomb in St Peter's Basilica.
This led to a popular Roman saying, "Quer che nun fecero li Barberi lo fecero i Barberini" - that which the Barbarians couldn't do was done by the Barberini!

Since the Renaissance period the Pantheon has been used as a tomb, and some great names, like Raphael and the Italian kings Vittorio Emanuele II and Umberto I, have chosen this as their final resting place.

The Pantheon remains a church, and to this day masses and weddings are celebrated.

Roman Pantheon Architecture



The classical styles of Ancient Greece were kept alive in many Ancient Rome buildings, and the Roman Pantheon Architecture with its rectangular Portico and Corinthian Columns is an excellent example:

There are 3 rows of columns supporting the Portico and Pediment (from the original Pantheon). The main structure is circular with a diameter of 43,3m (142 feet), and 6m (19 feet) thick walls support the dome which is a perfect half sphere. The height is 43,3 m, identical to its diameter, which means that if there was another identical dome beneath the present one it would make a perfect sphere.

The dome center contains a 9m (27 feet) diameter oculus (hole) to let light in and smoke out, and is symbolic of the sun. The coffered ceiling was meant to symbolize the heavens, but more importantly it helped to lessen the immense weight of the dome.
To this day engineers continue to marvel at the Roman Pantheon Architecture and how the dome stands - considering the forces and the fact that Romans didn't have reinforced concrete!

You see, concrete has a very low tensile strength, simply stated it can't bend well. Wood performs a little better but steel is the way to go.
Take a piece of foamalite (that white stuff they sometimes use for packaging), bend it, and like concrete it will suddenly snap - not good! Now put a knitting needle through the foamalite and try to snap it! Get the picture? That's what reinforcement does in concrete.



Generally speaking, the recipe for concrete is sand, stone and cement (the Romans would have used ash and lime instead of cement) mix this together with water, and allow to set for up to a month. The problem with traditional concrete is that it's very heavy; a large portion of the weight coming from the aggregate (stone). The Romans, in order to get around this problem in the Roman Pantheon Architecture they:

Reduced the weight of the concrete by using light weight aggregates like Tufa and Pumice

designed a coffered (indented) structure to reduce the volume of the dome and therefore the total weight

Incrementally reduced the thickness of the dome, from 6,4m (21ft) at the supporting walls to 1,2m (4ft) at the oculus, through a series of rings

designed a hole (oculus) in the center of the dome which further reduces the weight at which would be the furthest point from the supports and therefore the point of maximum forces (or moments).

poured (cast) the concrete for the Pantheon dome over a wooden supporting frame and utmost attention was given to compacting all the air (bad) out of the concrete. This would give the strongest possible set concrete.


The beauty of the dome, or any half sphere shape, is that it's essentially a series of arches (take an arch, hold it at the top and spin it around its central point thereby producing a series of several identical arches). The Romans had already mastered the arch and used its design extensively - the Roman bridges and aqueducts are good examples.

The problem with an arch is that at its base it pushes outwards, and unless you have a series of arches pushing against each other (as you do in the ancient Roman aqueducts) and canceling out each others pushing forces, you will end up needing a very large foundation or buttress.

The Pantheon dome, acting like many arches spun around a central point, would therefore also experience massive pushing out forces at its base (where it joins the supporting walls).

How did the Romans overcome this problem in the Roman Pantheon Architecture?

Have you ever wondered what those big bulky rings were around the base of the Pantheon dome? You guessed it. Their weight, and therefore downward and inward force, keeps the dome from pushing out and destroying itself.

This whole massive weight of the dome and its buttress-like rings are further supported through a series of arches and barrel vaults (very deep arches) around the perimeter of the supporting walls.

So there you have it, amongst many other things, the Romans invented light-weight concrete almost 1900 years before it was "rediscovered" by modern day engineers, and mastered coffering and the dome.