Romans admired Greek temples and borrowed the orders, but their great invention was a new way to enclose space. They used three tools together: the round arch, the vault (an arch extended into a tunnel, or two tunnels crossing, called a groin vault) and concrete, made of lime, volcanic ash called pozzolana, water and chunks of stone or brick. Roman concrete could be poured into wooden forms and even hardened underwater.
Key idea
Why it works
Looking closely: The Pont du Gard. Three tiers of arches carry a water channel across the Gardon River, about 49 meters above the riverbed. The bottom two tiers have big arches; the top tier has many small ones under the channel. It is built of huge stones fitted without mortar. Its beauty comes from repetition and proportion: arch after arch, the rhythm of a structure that does one job well.
Looking closely: The Pantheon. Look up. The dome is a perfect hemisphere of concrete, 43 meters across, and the floor is the same distance below its top, so a giant ball would fit inside. Five rings of sunken panels (coffers) shrink toward the top, lightening the dome and leading the eye to the oculus, an open circle about 9 meters wide. It is the only window: a disk of sunlight moves across the walls through the day, and rain falls through to drains in the floor. The builders made the concrete lighter as it rose, ending with pumice, a light volcanic stone, near the top. After nearly 1,900 years it is still the largest unreinforced concrete dome in the world.
Worked example: Read the inscription
- Agrippa built an earlier temple on the site, which burned.
- The present building was built under the emperor Hadrian, about AD 113 to 125.
- Hadrian kept Agrippa's name on the new porch.
Answer: Hadrian; the inscription honors Agrippa's earlier temple.
Common mistake