Groves Mausoleum and the Pantheon in Rome
By Peter Barratt
Apr 2, 2014 - 9:49:26 PM
The Pantheon and the Fontana del Pantheon.
The Pantheon with its portico and rotunda is the best preserved building dating from the pre-Christian era of the Roman Empire. It was built between 31 and 27 BC as a temple to ‘all the gods’ and its construction was part of an impressive building programme undertaken by the Roman Emperor The inscription on the architrave at the front of the building of today bears the inscription:
M·AGRIPPA·L·F·COS·TERTIUM·FECIT translated in full it means: "Marcus Agrippa, son of Lucius, constructed this building when consul for the third time."Though largely constructed of stone with very thick walls the original building was almost totally destroyed by fire and had to be re-built by the emperor Hadrian in 126 AD. The building was again destroyed early in the first century and was rebuilt largely in the form we see today by Trajan's architectApollodorus of Damascus. In 202 AD remarkably the building had to be repaired yet again, for which there is another, smaller but very informative inscription which reads: "PANTHEUM VETUSTATE CORRUPTUM CUM OMNI CULTU RESTITUERUNT" ('with every refinement they restored the Pantheon worn by age'). At this time it was just 229 years old.
Cross-section of the Pantheon in Rome showing
how a 43.3 m-diameter sphere fits under its dome
Many Roman temples were destroyed after the Emperor Constantine converted to Christianity in 325 AD. Fortunately, before the Pantheon could be demolished the Byzantine EmperorPhocasgave the building toPope Boniface IV, who converted it into a Christian church and consecrated it to Sancta Maria ad Martyres with the admonition “…so that the commemoration of the saints would take place henceforth where not gods but demons were formerly worshipped" (appropriately perhaps, the Pantheon was featured in the recent film ‘Angels and Demons’).
The building is one the great wonders of Roman architecture and took over three years to construct. The octastyle portico has three lines of monolithic granite columns eight columns abreast in the front row and two rows with four columns each. The unfluted monolithic columns have shafts 50Roman feethigh (weighing about 100 tons) with capitals that are 10 Roman feet tall in theCorinthian order. The marble for the unfluted columns was shipped from Egypt and dragged more than 100km from the quarry to the River Nile on wooden sledges. Then the columns were floated by barge down theriver in Egypt and transferred to sturdy wooden ships to cross theMediterranean Sea. At the Roman port ofOstia, they were transferred onto barges and pulled up theRiver Tiber to Rome. Once in Rome the columns were still about 700 metres from the building site and were dragged on rollers for erection on the prepared portico.
Floor plan of the Pantheon from Georg Dehio/Gustav von Bezold
The most significant element in this amazing building is the dome that was constructed of solid unreinforced concrete. (Banister Fletcher demurs on this point and says the dome construction was of brickwork with thick mortar). Since the dome is monolithic there is little lateral thrust but in any case the supporting rotunda wall is an average of 20ft wide more than enough to resist any lateral thrust. The dome features sunken coffered panels, in five concentric rings of 28 voissoirs (stones cut to the shape of their position in the dome). This was a monumental task and, it is presumed the coffer panels had symbolic meaning and originally the coffers may have contained bronze stars, rosettes, or other ornaments. Later these were removed by Pope Urban VIII and provided enough bronze to cast 110 cannon and provide enough bronze for the baldacchino over the high altar in St Peters Basilica.
The thickness of the dome varies from 6.4 metres (21ft) at the base of the dome to 1.2 metres (3.9ft) around the oculus – the 30ft diameter unglazed ‘eye’ in the centre of the dome. Studies have estimated that the dome containing the coffered voussoirs weighs about 4,535metric tons(5,000short tons). The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142ft), so that the whole interior would fit exactly within a three dimensional sphere 43.3 metres (142ft) in diameter.The Pantheon still holds the record for the world's largest unreinforced concrete dome and incidentally is 5 feet wider than the dome of St Peter’s Basilica.
The Pantheon Dome. The concrete for the coffered dome was poured in moulds, probably
mounted on temporary scaffolding. The oculus is the main source of natural light.
Throughout the day, the light from the oculus moves around the interior space with a sort of reverse sundial effect.This method of lighting is very effective even on the dullest of days. The oculus also serves as a cooling and ventilation medium. During storms, a drainage system below the floor handles the rain that falls through the oculus.
There are eight recesses on the inside of the rotunda wall one on which was the entrance (moved later to open to the north). Above the internal columns are hidden relieving arches to resist any possible outward thrust of the dome. The upper section inside the rotunda was plated with specially selected panels of stone separated by pilasters of porphyry and the massive bronze doors were originally covered with gold. Circles and squares form the unifying theme of the interior design. The checkerboard floor pattern contrasts with the concentric circles of square coffers in the dome. Each zone of the interior, from floor to ceiling, is subdivided according to a different scheme. This discordance has not always been appreciated, and the attic level was redone according to Neoclassical taste in the 18th century.
The interior of the Pantheon in the 18th century,
painted by Giovanni Paolo Panini
The Pantheon is a favourite subject for architectural students. Fortunately, because the building obeyed the classical rules of proportion, it is not necessary to hire a ladder or a cherry-picker to measure the height. The column base diameter provided the module upon which all other architectural elements are based. And, of course, the great architectural historian, Bannister Fletcher, provided a scaled plan, building sections and dimensions (in Imperial measure – not Roman feet!) for students to be able to double check their measured work.
Sources: Banister Fletcher, A History of Architecture, Batsford, London, 1950, Will Durant, Caesar and Christ, Simon and Schuster, New York, 1944 and Wikipedia (various citations).
© Peter Barratt RIBA Dipl.Arch.(Birm) MCP
Peter Barratt is an architect/town planner who was formerly in charge of the
development of Freeport. He writes with first-hand knowledge of the Bahamas
having first visited the country in 1960. Because of his long experience in the
islands he has been able to record many interesting insights, observations and
historic moments that readers should find intriguing. He has published several books
about the island nation:
Freeport Notebook and
(the latter a historical novel about the islands). He has also written a full
colour work entitled:
and two other works are near publication:
Port at War and
St Peter Was Never There
The views expressed here are solely those of the author in his/her
private capacity and do not in any way represent the views of
A measured drawing of the Pantheon by the author while a student at Birmingham School of Architecture
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