Ancient Rome greatly influenced architecture, and continues as a major influence even today. One architectural feature which Rome perfected is the arch. Romans did not invent the arch, but they greatly expanded its use and designed arches that could support massive amounts of weight. Roman arches are comprised of several parts.
The keystone, or capstone, is the center stone found at the top of the arch. In this position it supports the surrounding bricks or stones and helps distribute the weight of the remainder of the arch. Its name "keystone" comes from its importance: without it, the arch would collapse. Romans were the first to use keystones in their arches.
The keystone is surrounded on each side by voussoirs, or wedge-shaped bricks or stones. The term voussoir comes from French and Latin roots meaning "to turn." The thrust of the voussoirs pushes outward and downward in a Roman arch. Roman arches are noted for their semi-circular, non-pointed curves. The use of voussoirs creates arches which can be be used to span large distances and which can bear heavy loads. An example of this can be seen in the arches used in construction of ancient Roman aqueducts, many of which still stand today.
The keystone and voussoirs of an arch need a base on which to rest. These bases are called piers. A Roman arch's pier is the wall or stone on which the arch rests. Concrete and stone were often used in the construction of piers, which are usually square or rectangular in shape.
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