Arch

An arch is a curved vertical structure spanning an open space underneath it. Arches may support the load above them, or they may perform a purely decorative role. As a decorative element, the arch dates back to the 4th millennium BC, but structural load-bearing arches became popular only after their adoption by the Ancient Romans in the 4th century BC. Arch-like structures can be horizontal, like an arch dam that withstands a horizontal hydrostatic pressure load. Arches are usually used as supports for many types of vaults, with the barrel vault in particular being a continuous arch. Extensive use of arches and vaults characterizes an arcuated construction, as opposed to the trabeated system, where, like in the architectures of ancient Greece, China, and Japan (as well as the modern steel-framed technique), posts and beams dominate. The arch had several advantages over the lintel, especially in masonry construction: with the same amount of material an arch can have larger span, carry more weight, and can be made from smaller and thus more manageable pieces. Its role in construction was diminished in the middle of the 19th century with introduction of wrought iron (and later steel): the high tensile strength of these new materials made long lintels possible.