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A barrel vault, also known as a tunnel vault or a wagon vault, is an architectural element formed by the extrusion of a single curve (or pair of curves, in the case of a pointed barrel vault) along a given distance. The curves are typically circular in shape, lending a semi-cylindrical appearance to the total design. The barrel vault is the simplest form of a vault: effectively a series of arches placed side by side, i.e., one after another. It is a form of barrel roof. As with all arch-based constructions, there is an outward thrust generated against the walls underneath a barrel vault. There are several mechanisms for absorbing this thrust. One is, of course, to make the walls exceedingly thick and strong - this is a primitive and sometimes unacceptable method. A more elegant method is to build two or more vaults parallel to each other; the forces of their outward thrusts will thus negate each other. This method was most often used in construction of churches, where several vaulted naves ran parallel down the length of the building. However, the outer walls of the outermost vault would still have to be quite strong or reinforced by buttressing. The third and most elegant mechanism to resist the lateral thrust was to create an intersection of two barrel vaults at right angles, thus forming a groin vault. Barrel vaults are known from Ancient Egypt, and were used extensively in Roman architecture. They were also used to replace the Cloaca Maxima with a system of underground sewers. Early barrel vault designs occur in northern Europe, Turkey, Morocco and other regions. In medieval Europe the barrel vault was an important element of stone construction in monasteries, castles, tower houses and other structures. This form of design is observed in cellars, crypts, long hallways, cloisters and even great halls. ==Theory and early history== Barrel vaulting was known and employed by early civilizations, including Ancient Egypt and Mesopotamia, but apparently it was not a very popular or very common method of construction. The technique probably evolved out of necessity to roof buildings with masonry elements such as bricks or stone blocks in areas where timber and wood were scarce. The earliest known example of a vault is a tunnel vault found under the Sumerian ziggurat at Nippur in Babylonia, ascribed to about 4000 BC, which was built of burnt bricks amalgamated with clay mortar. The earliest tunnel vaults in Egypt are found at Requagnah and Denderah, from around 3500 BC; these were built in sun-dried brick in three rings over passages descending to tombs: in these cases, as the span of the vault was only two metres. In these early instances, the barrel vault was chiefly used for underground structures such as drains and sewers, though several buildings of the great Late Egyptian mortuary palace-temple of Ramesseum were also vaulted in this way.〔Dietrich Wildung, ''Egypt, From Prehistory to the Romans'', Taschen, 2001.〕 Recent archaeological evidence discovered at the Morgantina site (in the province of Enna) shows that the aboveground barrel vault was known and used in Hellenistic Sicily in 3rd Century BC, indicating that the technique was also known to Ancient Greeks. Ancient Romans most probably inherited their knowledge of barrel vaulting from Etruscans. Romans were the first to use this building method extensively on large-scale projects, and were probably the first to use scaffolding to aid them in construction of vaults spanning over widths greater than anything seen before. However, Roman builders gradually began to prefer the use of groin vault; though more complex to erect, this type of vault did not require heavy, thick walls for support (see below), and thus allowed for more spacious buildings with greater openings and much more light inside, such as ''thermae''. After the fall of the Roman empire, few buildings large enough to require much in the way of vaulting were built for several centuries. In the early Romanesque period, a return to stone barrel vaults was seen for the first great cathedrals; their interiors were fairly dark, due to thick, heavy walls needed to support the vault. One of the largest and most famous churches enclosed from above by a vast barrel vault was the church of Cluny Abbey, built between the 11th and 12th centuries. In 13th and 14th Century, with the advance of the new Gothic style, barrel vaulting became almost extinct in constructions of great Gothic cathedrals; groin vaults reinforced by stone ribs were mostly used in the beginning, and later on various types of spectacular, ornate and complex medieval vaults were developed. However, with the coming of the Renaissance and the Baroque style, and revived interest in art and architecture of antiquity, barrel vaulting was re-introduced on a truly grandiose scale, and employed in the construction of many famous buildings and churches, such as Basilica di Sant'Andrea di Mantova by Leone Battista Alberti, San Giorgio Maggiore by Andrea Palladio, and perhaps most glorious of all, St. Peter's Basilica in Rome, where a huge barrel vault spans the -wide nave.〔http://www.stpetersbasilica.org/Interior/Nave/Nave.htm〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「barrel vault」の詳細全文を読む スポンサード リンク
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