the keystone arch was used by almost every early civilization. to build a keystone arch , stones are cut so that the opposite sides taper toward each other sightly . the upper and lower surfaces are carved so that when several stones are placed side by side , the upper and lower surfaces meet in smooth, continuous curve. some form of scaffolding is built under the arch and shaped to accept the curved underside of the stones, them the stones are fitted in place one by one . the keystone is the top center stone, the last to be dropped into position, afterwards, the scaffolding is removed and the arch is self-supporting.the basic principles of building keystone archesthe uses of arches in modern architecturethe role of scaffolding in building keystone arches
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