Arch
Arches were originally developed as a means of providing interior support to buildings, and creating doors and windows. Their use in construction permitted longer single spans built from smaller, more easily handled units, rather than from huge separate beams.
The earliest forerunner of the arch consisted of two vertical pillars with an interlocking beam. Both pillar and beam were made of wood or stone. The Babylonians used arches as early as the sixth century B.C., as did the Egyptians, Chinese, and Greeks.
As urban centers grew and the need for larger buildings increased, larger pillars and beams were used to build temples, courts, and public baths. When it became more and more difficult to work with the enormous pillars and beams, true arches, curved overhead and made of small units stacked on top of one another, came into use. The stacking technique made massive arches possible, since blocks could be hauled in one at a time and handled more easily.
The Roman Empire initiated large projects using sophisticated archwork. Its quest to create an elaborate system of public works demanded large numbers of buildings, highways, and aqueducts. Efficiency was a key component of a project of that scale, and the Roman arch, with its characteristic keystone at the top locking the arch into place, answered that demand, holding loads firmly yet remaining simple to construct. The Romans also used concrete extensively, bracing arches with cross vaults where immense loads demanded it. Reliance on cross-vaulting led to the construction of domes--essentially three-dimensional arches.
The Roman arch, an example of form following function, was massive and perhaps a bit monotonous in appearance. By the twelfth century the Gothic arch, characterized by a point and often relying on a joint at the apex rather than a keystone, began to appear in Europe, primarily in the design of the continent's great cathedrals. The Gothic arch was part of a trend toward a greater diversity in design which employed vaulted ceilings, flying buttresses, large stained glass windows, and ledges for statuary.
Arches were used extensively in bridge construction, with stone arches used during the Roman Empire and again in Europe from medieval times to the present. During the 1700s and 1800s, iron replaced stone in bridge-building, and by the mid-1800s, steel arches came into use to support the increased loads created by trains and longer spans.
While modern architects seldom use arches, a few examples can be found such as the unique Gateway Arch in St. Louis. Designed by Eero Saarinen (1910-1961) and completed in 1965, the stainless steel arch stands at a height of 630 ft (220 m) alongside the Mississippi River, attracting tourists and sightseers. The world's longest arch spans are the Sidney Harbor Bridge in Australia and the Bayone Bridge over the Kill van Kull in Bayone, New Jersey, with spans of 1650 ft (502.9 m) and 1652 ft (503.5 m) respectively.
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