Pantheon - Table of Contents   ...........  Architecture Around the World

2002 photos
Exterior - Pantheon

Rome, Italy
Erected 18-128 C.E.

The supreme example of Roman structural ingenuity—and its aesthetic apogee - is the Pantheon. Built by the emperor Hadrian to replace an earlier temple by Agrippa, the Pantheon still stands, virtually unchanged for almost 1,900 years. Its dome was the widest until the nineteenth century.

With its soaring rotunda, the Pantheon is the most beautiful of Roman buildings. In terms of engineering, it is a daring creation since the dome exerts 5,000 tons of pressure on 20-foot-thick walls. The building's blend of enormous interior space, concrete construction, and traditional classical forms makes it the most imitated of Roman edifices.

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Portico

 

40' high red-gray granite
Corinthian columns taken from an Egyptian temple.

Corinthian columns with Corinthian pilaster on right.

Corinthian pilasters

Modillions (near top of photo). Corinthian pilasters

Modillions



Corinthian capital



The design is a hybrid. Its pedimented porch and Corinthian columns are Greek, while the soaring rotunda - unsuspected from the outside - is pure Roman. This synthesis became the model for countless succeeding buildings, from St. Peter's in the Renaissance to designs by Palladio and Thomas Jefferson.

The Dome

Five thousand tons of concrete shape the dome, but the content of the concrete varied to lighten the load as it ascended. Mixed with heavy basalt at the bottom, the layers contained porous, lightweight pumice at the top. The coffers, or recessed panels, of the dome also diminish in size and depth as the dome rises. This decrease creates a false perspective to make the dome seem even higher, while the coffering itself lightens the weight of the domed shell. The sole supports of the dome are sixteen barrel vaults channeling weight to eight piers, disguised by cosmetic columns.

Roman Arches

Philosopher Alfred North Whitehead wrote, "The Roman Empire existed by virtue of the grandest application of technology that the world had hitherto seen." This technology included engineering innovations like the arch, vault, and dome. For the first time, Roman builders spanned huge volumes of interior space, shaping an architecture of enclosed voids, not supporting mass. With the invention of concrete, they built increasingly daring forms, from baths to basilicas, on a vast scale.

The essential ingredient of Roman building was the arch. Although Romans were smitten by "superior" Greek style and plastered conspicuous columns on facades, they abandoned the column as an actual structural support.

The arch and its progeny - the vault and the dome - revolutionized architecture. A stone lintel atop two columns rarely spans a distance as wide as 15 feet, but an arch can span 150 feet. Additionally, when its keystone is locked into place, the arch supports itself as well as immense loads on top. Combined with concrete, which could be cast in molds of any shape and scale, the arch allowed Romans to enclose enormous spaces and fully exploit the potential of these new forms and materials.

When an arch is extended in a straight line, or multiplied in depth, it becomes a barrel (or tunnel) vault. Such vaults provide a curved ceiling over two parallel walls and may be combined to form arcades (as in the Coliseum) supporting multiple tiers of superstructure. When two barrel vaults intersect at a right angle, the juncture forms a groin or cross-vault, which provides lunette windows for lighting at either end. An arch, rotated 360 degrees, creates a dome. By the first century B.C.E., the arch and vault were pervasive in Roman buildings.

Ancient concrete was not liquid but a viscous mixture of sand, lime, water, and aggregate. It was laid down in layers inside wooden or brick form work and solidified into a dense artificial stone that was light, strong, fireproof, and monolithic. Roman concrete walls and shells were always lined on both the exterior and interior with brick or a veneer of decorative stucco, fresco, mosaic, or marble. Purely ornamental columns, like olives dressing up a plain salad, adorned arches for a touch of Greek zest. The columns were generally engaged, or partially embedded in walls. When flattened and squared off, they are known as pilasters.


Sources:


Photos and their arrangement 2002 Chuck LaChiusa
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