The arch, one of the basic architectural forms, is a curved structure that spans an opening. Arches can be functional—for example, they can support a wall—or they can be decorative. The Romans used arches extensively in the construction of aqueducts, amphitheaters, bridges, and domed temples.

For centuries, the peoples of the ancient Middle East and Mediterranean used vertical supports* topped by horizontal beams in the construction of doorways and gates. The Greeks also developed a corbeled (or stepped) arch. The Lion Gate at Mycenae in Greece is an example of this early form of arch. Corbeled arches were built with rows of blocks on either side of the opening, each jutting out a little farther over the row below until the two sides met in the middle at the top of the arch.

A true arch consists of vertical supports with blocks arranged in a semicircle across the opening. The Egyptians used the arch as early as 2700 B.C., mainly in tombs and other small structures. The Mesopotamians used arches for their city gates. Although the Greeks understood the principle of the arch, they did not combine it with other architectural elements until the 300s B.C.

* vertical support upright beam or column that serves as a base in construction

The early Romans learned about arches from the Etruscans, their neighbors in central Italy. The Etruscans taught the Romans how to build bridges, drainage systems, and aqueducts, all using arches. The Romans further developed the arch, using wedge-shaped blocks (called voussoirs) to form a curve across the top of the arch. The curved section rested firmly on two vertical supports. The last stone to be inserted was the keystone, the topmost center stone. The pressure of the other stones against the keystone helped to support the arch. This arch, which was stronger than earlier types of openings, led to the development of the vault*.

Working in mortar*, concrete, and stone, the Romans built thousands of structures that featured arches and vaults. Their creative use of these elements revolutionized architecture. Several famous examples of Roman arch and vault technique can be seen today. They are the Pont du Gard in southern France (a huge aqueduct dating from the early first century A.D.), the exterior of the Colosseum, and the Arch of Constantine commemorating the emperor’s victory over Maxentius in A.D. 312. Sculpted scenes of the emperor’s campaign decorate the sides and top of this triumphal* arch. (See also Aqueducts; Architecture, Roman; Constantine.)

* vault arched ceiling or roof

* mortar mixture of lime, cement, sand, and water that is placed between stones to hold them together

* triumphal refers to the ancient Roman ceremony during which a victorious general enters the city

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