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Imperium in the Pantheon of Rome and its Pavimentum

Posted by Patrick Hunt

Pantheon from Hadrianic Rome c. 125 CE to Modern time

Few great buildings in the world have a history parallel to the Pantheon; none are so glorious to better represent the genius of Roman architecture. Even in its altered state where much of its outer decoration has been stripped over the millennia and its incredible interior modified, the Pantheon still exemplifies the Roman aim for perfection in structural integrity and philosophical harmony. Three points are notable at the outset of this essay: The Pantheon is a remarkable achievement of 1) Roman engineering, 2) sacred geometry and cosmography and 3) as a statement of political imperium and Roman stability. Dio Cassius (c. 220 CE) said, “Thanks to its dome it resembles the vault of heaven itself.” But it is mostly the floor – the pavimentum - that will be newly interpreted as a statement of imperium in this brief architectural essay.

The Pantheon temple to “all the gods” [pan theon] was originally part of Augustus Caesar’s plan to rebuild Rome in his image. Marcus Agrippa, friend and general of Augustus, likely designed the first Pantheon, and his inscription still fills the architrave above the portico from when he (“son of Lucius”) was consul in Rome for the third time [M∙ AGRIPPA∙ L∙ F ∙ COS ∙TERTIUM ∙FECIT]. Agrippa originally built it as an ovatio ("non-military triumph") to Augustus but the philhellene emperor Hadrian transformed and finished the rebuilt monumental temple a century later around 122-24 C.E. He may have envisioned it as a personal Pythagorean philosophical summation of what a Roman monument should entail and mean in its Greek name and cosmopolitan Roman structure as an imperial statement of power. Hadrian also intended the use of Agrippa’s memorial to show his own connection to former Augustan glory.

Original Interior of the Pantheon as reconstructed in virtual reality

In its sacred geometry, it has three main architectural components. A rectangular portico or porch with its triangular pediment connects to a cylindrical drum in the cella or main temple structure, and is surmounted by a rotunda or dome. Thus it contains the basic Pythagorean units. Viewers could see the sacred geometry of the cosmos in the triangle of pedimental portico roof, rectangle of portico and hemisphere of roof that actually becomes a full sphere in that space between roof and marble floor. This is a perfect 44-meter [around 150 ft.] sphere matching the 44-meter width of the cylindrical main cella. Hadrian intended its mathematical polygons to be harmoniously integrated, although the portico may not be as carefully connected to the drum as is the marvelous rotunda. The 9 meter (around 30 feet) diameter oculus in the ceiling serves as a mirror of the round heaven – appropriately open to the sky - and its graduated ribbed ceiling coffers immediately below corresponded to the five planetary gods.

Pantheon Interior looking up into the oculus (heavenly symbolism)

For its engineering genius, the Pantheon’s construction includes composite materials such as brick, concrete, tufa, basalt, pumice, granite columns, and leaded bronze roof, with much of the structure veneered inside and outside with marble over seven arched alcoves. The primary external marble veneer was white whereas the interior veneer was multi-colored. Well-planned foundations are of volcanic-related stone including basalt, with walls of tufa (in this case compressed volcanic ash), brick and concrete, and coffered ceiling of light pumice covered with leaded bronze sheets. Basalt is the optimum foundation stone with its great compressive strength; pumice concrete equally understood as optimum for ceilings with its durable lightness. Thus the structure proceeds from bottom to top in ever lighter materials which have served it well for durability.

Original Pantheon pavimentum as reconstructed in virtual reality

In its statement of imperium, even the marble inlaid opus sectile floor shows stone from all over the empire, even though such use of these marbles is by no means the earliest example of these individual marbles, rather it is more important that all are used simultaneously in this and other earlier as well as contemporary Roman contexts. The specific marbles here suggested as related to the idea of imperium include purple Imperial Porphyry from Egypt (Mons Porphyrites), Docimian pavonazzetto from Asia Minor (Marmor docimenium) and yellow Giallo Numidiana marble from Carthage (Marmor numidicum) and - perhaps to complete a Mediterranean "square" - an as-yet unprovenanced gray Granito Grigio probably from the northwest (Pyrenees, Gaul or the Alps?). Thus all four corners of the Roman Mediterranean (Mare Nostrum) world could be shown on the pavimentum floor as a squared circle as in the geography of Ptolemy, much like the Pantheon floor patterns. These opus sectile patterns are in repeated squares and circles that echo the overall structural geometric shapes of the building design. This geographical stone representation from the four corners of the empire is also significant because these floor stones can be understood as spolia expressing conquest of Egypt, Asia, Carthage and Gaul. Conquest of Greece is implied as well in the green Lapis Lacadaemoni[u]s bands (seen in the walls parallel to and including the frieze units in the arced and pedimented aediculae), truly a “government program translated into stone” (Bernard Andreae).

Map of Roman Empire around time of Trajan to Hadrian (circa 117-125 CE)

Imperial Porphyry from Egypt (southeast)
Giallo Numidiana from west Numidian Carthage region (southwest)
Docimian Pavonazzetta from Asia Minor (northeast)
Grey Granite from Gaul/Alps (northwest)?

Images of Pantheon in cross section and spherical mathematical modeling

Link to 360 degree floor view, somewhat truncated but good marble plan:
(thanks to Peter Watts for the link)

After Rome became Christianized, the Pantheon became the Church of Santa Maria Rotunda, consecrated by command of the Byzantine emperor Phocas in 609 C.E., although the much later 17th c. dual towers – wrongly assigned to Bernini - were removed only a few generations ago. Although it has been altered and partly stripped by later Roman noble houses – producing the quip, “What the barbarians did not dare desecrate, the Barberini did”, the Pantheon now also contains the tombs of Raphael and Italian kings such as Vittorio Emmanuelle (partially reintegrated in 1878) that obscure the numerous original internal Roman apses containing shrines for major and minor gods. The entire internal volume of the monument was 1520 square meters without any reinforcing support. No structure had eclipsed the vast internal diameter of its rotunda dome until the 20th c. Although Brunelleschi with the Duomo of Florence [42 m] around 1420-30 and Bramante and Michelangelo in St. Peter’s [42 m] in Rome (between 1514-1564), Sir Christopher Wren in St. Paul's in London in 1674 [around 30 m] and many others - including Les Invalides in Paris and the U.S. Capitol in Washington D.C. - attempted unsuccessfully to eclipse the Pantheon dome, it remains the finest rotunda in the world. It is almost universally accepted that the massive Pantheon is the most impressive surviving Roman monumental building in the world.

(Note: This essay is a copy of many lectures at Stanford University since 1994 and previously published in a prior version by Patrick Hunt. "Pantheon" in Encyclopedia of the Ancient World, Salem Press, 2002, 868)


Jean-Pierre Adam. Roman Construction: Material and Techniques. Paris: Picard, 3rd ed. 1995.

Bernard Andreae. “Pantheon” in The Art of Rome. New York: Abrams, 1977, 513-15.

Axel Boethius. Etruscan and Early Roman Architecture. New Haven: Yale University Press, 1994 impression, 235n27.

Gabriele Borghini, ed. Marmi antichi. Rome: Ministero per i Beni Culturali e Ambientale/ Edizioni de Luca, 1997, 214 pl.65, 264 pl.109, 274 pl.116.

Amanda Claridge. Rome: Oxford Archaeological Guides. Oxford: Oxford University Press, 1998, 201-6.

Patrick Hunt. “Pantheon” in Encyclopedia of the Ancient World, Salem Press, 2002, 868.

William L. Macdonald. The Pantheon: Design, Meaning and Progeny. Cambridge, MA: Harvard [1976] 1998 repr.

Henri Stierling. The Roman Empire, vol. I. “The Pantheon”, pp. 153-8. Cologne: Taschen, 1996.

John Ward-Perkins. "Tripolitania and the Marble Trade" in Journal of Roman Studies 41 (1951) 88-104, esp. 96 & ff.

Photo and image credits:

Modern photo of Pantheon from

Virtual reality images of Pantheon:

Oculus photo by Thomas Slijper, Netherlands

Mathematical interior from Gert Sperling “The Quadrivium in the Pantheon of Rome”, Fuldatal, Germany.
Map of Roman Empire from

Stanford University

Patrick Hunt © 2005


I would like to know if the Oculus could have been used as a calendar to mark the seasons as the earth rotated on its axis as well as the 13 phases of the moon.

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