Engines of Our Ingenuity

No. 2810: THE CONCRETE REVOLUTION

by Richard Armstrong

Today, some concrete achievements. The Honors College at the University of Houston presents this program about the machines that make our civilization run, and the people whose ingenuity created them.

Let's compare two famous buildings: The Parthenon in Athens and the Pantheon in Rome. The Parthenon is a huge temple, rectangular in form and fairly basic in design. A forest of Doric columns holds up a sloped roof, which stands over the building where the cult statue of the goddess resides. It's made of hewn blocks, quarried on Mount Pentelikon, laboriously transported to the acropolis and clamped together. Now consider the Pantheon: although it appears similar from the front with its porch of columns supporting a sloping roof, this porch is attached to a massive cylindrical building, covered by a breathtaking coffered dome. Through the circular opening at the dome's apex, sunlight beams in, revealing the immense volume contained by the structure. Instead of a dark inner sanctum, we enter an expansive, ethereal space. This is the miracle of concrete.

The Parthenon
UH Architecture student admiring the Pantheon in Rome. Photo by Richard Armstrong

From the second century BC through the second century AD, the ancient world went through what's been called the Concrete Revolution. The Romans' dynamic civilization required ever larger and sturdier structures, and they excelled in the use of concrete to make buildings that would have been unthinkable before their time.

Roman concrete isn't the runny stuff you see poured for sidewalks today. It's a combination of fill often made up of largish stones, sometimes tiles and other bits of rubble; then there's lime, sand, and pozzolana, a volcanic ash that was the magic ingredient. When this was mixed together and allowed to set, the result would be much harder than its parts; it could even be poured under water. This made possible not only the construction of better temples and basilicas, but also aqueducts, piers, and whole artificial harbors, like Ostia and Caesarea. Buildings could be made in almost any shape, no longer restricted to the sharp angularities of cut stone and pillars. Barreled and ribbed vaults could give an airy quality to structures that were at the same time vast and imposing, like the Colosseum. Best yet, one could build solidly and quickly.


Roman concrete with brick facing (opus testaceum or latericium) on the Palatine Hill in Rome. Photo by Richard Armstrong

Anyone visiting a Roman ruin will be struck by the varied appearance of Roman concrete. This is because the wall core could be faced with a variety of things. Sometimes square-ended stones were used, set diamond-wise to give the appearance of a fishnet. Sometimes brick facing was used, either along the whole surface or just at the corners to sharpen the form. Quite often the facing didn't matter, since once the wall was finished, it was stuccoed over and painted with vibrant frescoes, or covered with marble to make the whole construction look solid, costly, divine.

The Pantheon's dome is one of the greatest concrete achievements of all time; it has lasted for centuries in spite of fires, earthquakes, bombings. It's all the more remarkable when you consider its concrete is not reinforced. No iron rods secure its mass as it rises to a height of 142 feet above you. That's when you realize: Roman concrete was an expression of supreme self-confidence.

I'm Richard Armstrong, at the University of Houston, where we're interested in the way inventive minds work.

(Theme music)



The net-like opus reticulatum combined with brickwork in Pompeii. (Modern reconstruction from the lintel upwards). Photo by Richard Armstrong.

See also Engines episode 1345, The Pantheon.

Sources:

For a Roman account of building materials and techniques, see Vitruvius On Architecture Book 2:3-8. Loeb edition with translation by Frank Granger, Harvard UP, 1931. Vol. 1

See the lecture online by Yale Professor Diana Kleiner, "Technology and Revolution in Roman Architecture." http://videolectures.net/yalehsar252s09_kleiner_lec03/

You can see video constructions of the Parthenon at: http://www.youtube.com/watch?v=cy5G28DsDKo http://www.youtube.com/watch?v=7YDKTLQSs8M

You can also see animated reconstructions of Roman buildings (set to the soundtrack of Gladiator) here (Pantheon begins at 4:05): http://www.youtube.com/watch?v=UzAhpdo4RSI

Adam, Jean Pierre. Roman Building: Materials and Techniques. Translated by Anthony Matthews. Indiana UP, 1994.

Ball, Larry. The Domus Aurea and the Roman Architectural Revolution. Cambridge UP, 2003.

Lancaster, Lynne. Concrete Vaulted Construction in Ancient Rome: Innovations in Context. Cambridge UP, 2005.

This episode was first aired on July 18, 2012



The Engines of Our Ingenuity is Copyright © 1988-2012 by John H. Lienhard.