Today we build a big room. The University of
Houston's College of Engineering presents this
series about the machines that make our
civilization run, and the people whose ingenuity
You might say the
fundamental problem of architecture is creating
interior space. Igloos and wigwams offer clever means for
gaining unobstructed indoor space. Houses offer
more space, but that space has to be broken up into
rooms. That's okay, because it affords some
privacy. The large unobstructed space offered by
Indian and Neolithic long houses was awkwardly long
How then to create indoor spaces, as wide as they
are deep, spaces for large gatherings: temples,
churches, closed arenas, assembly halls? The
Egyptians didn't manage it. Greek architecture
didn't provide that sort of indoor space either.
The Romans finally succeeded because they had the
concept of the Roman arch.
In 25 BC, Agrippa dedicated the Pantheon to
all the gods. The word Pantheon means of all
gods. But that didn't incur proper divine
protection for the wooden building against
destructive fires in 80 and again in AD 110.
Hadrian was emperor of Rome during the second fire.
He was an extremely effective leader, a great
builder, and a fine architect.
It was under Hadrian's rule that Hadrian's Wall
across Northern England was begun. It was under
Hadrian, and with his involvement as an architect,
that a new Pantheon was erected in AD 126. And it
became one of the architectural landmarks of all
The Pantheon is a large pillbox of a building with
a square classical front on one side. You enter
that front, and it leads you into the largest domed
space the world would see until 1800 years later.
The central chamber is 142 feet in diameter, and
its top rides 142 feet above the floor. But that's
This is no Gothic arch of stacked stone. It's a far
more modern construction. The dome is cast
concrete, decorated with an elaborate waffle
pattern on the inside. At the top is another
surprise. The center is a 27-foot hole -- an
oculus, or eye, which carries light into
that great inner space. The 20th-century American
artist James Turrell has been using that idea.
Turrell has created many structures with apertures
in their roofs to catch the shifting lights of day
and of the half light in just the same way.
The cast concrete dome seems to've originated with
Hadrian. Previous attempts to build with concrete
had warned the Romans to make serious changes in
the way they used concrete. So the Pantheon sits on
a foundation ring 15 feet deep and 24 feet wide and
is buttressed by concentric outer support rings.
The shell of the huge dome not only tapers from a
thickness of 22 feet down to five feet. But the
engineers have also graded the density of the
concrete so the material is lighter near the top.
During the seventh century, in now-Christianized
Rome, this temple to all gods became the Rotunda of
Santa Maria. In that role it may command less
attention than Notre Dame or St. Peter's. But ask
anyone who's taken time to see that great skylit
hemispherical space. They will tell of being caught
off-guard by its surpassing ancient glory.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
The Builders: Marvels of Engineering
(Elizabeth L. Newhouse, ed.). Washington, D.C.: The
National Geographic Society, Book Division, 1992, pp.
History of World Architecture (Luigi Nervi,
ed.). New York: Harry N. Abrams, Inc., Publishers,
1974. This offers a good deal of material on the
Pantheon. See the Index.
Rivoira, G. T., Roman Architecture. New
York: Hacker Art Books, 1972, Chapter VIII,
See also Encyclopaedia Britannica articles
on Pantheon and Hadrian.