The Pantheon
Michelangelo once described the design of the Pantheon as an "Angelic and not human design". A Greek word meaning "to honor all Gods", the Pantheon is shaped very much like a dome covering the top of a barrel. When completed around 128 A.D., the Pantheon's clear span, concrete dome covered an area larger than half of a football field and remained unsurpassed in size until the 19th Century.
At the center of the dome is a bronze ring nine meters in diameter, called the oculus, which is open to the sky and illuminates the Pantheon's interior.
The dome is so carefully proportioned that its interior diameter of 142.4 feet (43.4 meters), is the same as the distance from the floor to the top of the oculus. The interior of the Pantheon dome consists of 140 concrete panels called coffers, arranged in a series of five bands, which suspend the oculus in place.
To lighten the dome's weight, the Romans tapered the coffers in thickness from 19'-8" (5.9 m) at the outer most band to less than 5 feet (1.5 m) at the innermost band and produced an early version of lightweight concrete using volcanic pumice as aggregate.
In the 5th Century the Vandals sacked and burned Rome. Upon entering the Pantheon, it is said that they fell silent before its grandeur and left it unspoiled. Most remarkably, the Pantheon has stood virtually unchanged for almost 1900 years without any metal reinforcing within its concrete dome or wall system.
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