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FROM TEMPLE TO CHURCH
The Roman Pantheon was originally built as a temple for all the gods.
Pan is Greek for “all” or “every” and theos is Greek for “god” (e.g.,
theology). Pantheism is a doctrine or religion that worships all gods.
After the A.D. 313 Edict of Milan established religious tolerance
throughout the Roman Empire, the city of Rome became the
center of the Christian world. By the 7th century, the Pantheon
had become St. Mary of the Martyrs, a Christian church.
A row of niches lines the rear walls of the Pantheon portico and
around the perimeter of the dome room. These niches may have
held sculptures of pagan gods, Roman emperors, or Christian saints.
The Pantheon was never early Christian architecture, yet the
structure was in the hands of the reigning Christian Pope. Pope
Urban VIII (1623-1644) pilfered precious metals from the structure,
and in return added two bell towers, which can be seen on some
photos and engravings before they were removed.
BIRD’S EYE VIEW
From above, the Pantheon’s 19-foot oculus, the hole at the top of the
dome, is an obvious opening to the elements. It allows sunlight into
the temple room below it, but also allows rain into the interior, which
is why the marble floor below curves outward to drain the water.
THE CONCRETE DOME
The ancient Romans were skilled at concrete construction. When
they built the Pantheon around A.D. 125 the skilled builders of Rome
applied advanced engineering to the Greek classical orders. They
gave their Pantheon massive 25-foot thick walls to support a huge
dome made of solid concrete. As the height of the dome rises, the
concrete was mixed with lighter and lighter stone material — the
top is largely pumice. With a diameter that measures 142 feet, the
dome of the Roman Pantheon ranks as the world’s largest dome
made of unreinforced solid concrete.
The “step-rings” can be seen on the outside of the dome.
Professional engineers like David Moore have suggested that the
Romans used corbeling techniques to construct the dome — like
a series of smaller and smaller washers set upon each other. “This
work took a long time,” Moore has written. “The cementing materials
properly cured and gained strength to support the next upper ring...
Each ring was built like a low Roman wall... The compression ring
(oculus) at the center of the dome... is made of 3 horizontal rings
of tile, set upright, one above the other... This ring is effective in
properly distributing the compression forces at this point.”
THE AMAZING DOME
AT THE ROMAN PANTHEON
The ceiling of the Pantheon dome has five symmetrical rows of 28
coffers (sunken panels) and a round oculus (opening) at the center.
Sunlight streaming through the oculus illuminates the Pantheon
rotunda. The coffered ceiling and oculus were not only decorative
but also lessened the weight load of the roof.
RELIEVING ARCHES
Although the dome is made of concrete, the walls are brick and
concrete. To support the weight of the upper walls and dome,
brick arches were built and can still be seen on the exterior walls.
They are called “relieving arches” or “discharging arches.”
“A relieving arch is usually of rough construction placed in a
wall, above an arch or any opening, to relieve it of much of the
superincumbent weight; also called a discharging arch.”
Penguin Dictionary of Architecture
These arches provided strength and support when niches were
carved out of the interior walls.