Arch, in the art of building, a series of stones or bricks arranged side by side in a curve in such a way that, if the two ends of the arc or bow be kept in place, the portions of the entire arch support each other. At first thought it would seem impossible to bridge a river with short stones or bricks, but if a framework of timbers be constructed with a curved surface on which the mason may build, the staging may be removed and the arch will not only stand, but will support any weight not great enough to crush the material of which it is built. The curvature of the arch causes a weight to act in a sidewise direction as a crushing, not a breaking force. Curved arches above windows and doorways were known certainly to the Egyptians and the Assyrians at least two centuries B. C. The Etrurians left cut stone arches. Where the Romans got the idea, nobody knows, but they were the first builders to bring the arch into general use. The Greeks were able to bridge a space no wider than the length of a single slab of stone; the Romans not only bridged windows and doorways, but wide halls. By the aid of the arch they built lofty domes and wide gateways. They carried their famous aqueducts across valleys over long series of stone arches. Their streets and public places were adorned with triumphal arches erected in memory of Titus, Severus, Constantine, and other distinguished conquerors. This custom has been followed in Paris and other European cities. The Dewey arch in New York City is perhaps the most prominent American example of this sort of thing. The round arch of the Romans was succeeded by the pointed arch of Gothic architecture, used in the beautiful cathedrals of western Europe, and by the Moorish arch employed in the Alhambra and other creations of Arabic genius. Modern arches have been constructed of concrete. The term is applied also to bow-like spans of iron work used in bridge construction. Arches of masonry carrying roadways are seen everywhere. One of the longest, but not the longest, span in the world, is that of the Cabin John bridge near Washington, D. C., 220 feet in length. A span at Plauen, Germany, is 295 feet long. The Eskimo employs the principle of the arch in building his snow huts. See ARCHITECTURE; BRIDGE; ESKIMO.