Discuss the various architectural innovations of the period: barrel and groin vaults, concrete, and the round arch.

What will be an ideal response?

Although the arch was known to cultures such as the Mesopotamians, the Egyptians, and the Greeks, it was the Romans who perfected it, evidently learning its principles from the Etruscans but developing those principles further. The Romans understood that much wider spans could be achieved with the round arch than with post-and-lintel construction. The weight of the masonry above the arch is displaced to the supporting upright elements (piers or jambs). The arch is constructed on a temporary supporting scaffolding and is formed with wedge-shaped blocks, called voussoirs, capped by a large, wedge-shaped stone, called the keystone, the last element put in place. The space inside the arch is called a bay. And the wall areas between the arches of an arcade are called spandrels. When a round arch is extended, it forms a barrel vault. To ensure that the downward pressure from the arches does not collapse the walls, a buttress support is often added. When two barrel vaults meet one another at a right angle, they form a groin vault. The interior corridors of the Colosseum in Rome use both barrel and groin vaulting.