Dome

A dome (from Latin: domus) is an architectural element that resembles the hollow upper half of a sphere. The precise definition has been a matter of controversy. There are also a wide variety of forms and specialized terms to describe them. A dome can rest upon a rotunda or drum, and can be supported by columns or piers that transition to the dome through squinches or pendentives. A lantern may cover an oculus and may itself have another dome. A dome (from Latin: domus) is an architectural element that resembles the hollow upper half of a sphere. The precise definition has been a matter of controversy. There are also a wide variety of forms and specialized terms to describe them. A dome can rest upon a rotunda or drum, and can be supported by columns or piers that transition to the dome through squinches or pendentives. A lantern may cover an oculus and may itself have another dome. Domes have a long architectural lineage that extends back into prehistory and they have been constructed from mud, snow, stone, wood, brick, concrete, metal, glass, and plastic over the centuries. The symbolism associated with domes includes mortuary, celestial, and governmental traditions that have likewise developed over time. Domes have been found from early Mesopotamia, which may explain the form's spread. They are found in Persian, Hellenistic, Roman, and Chinese architecture in the Ancient world, as well as among a number of contemporary indigenous building traditions. Dome structures were popular in Byzantine and medieval Islamic architecture, and there are numerous examples from Western Europe in the Middle Ages. The Renaissance architectural style spread from Italy in the Early modern period. Advancements in mathematics, materials, and production techniques since that time resulted in new dome types. The domes of the modern world can be found over religious buildings, legislative chambers, sports stadiums, and a variety of functional structures. The English word 'dome' ultimately derives from the ancient Greek and Latin domus ('house'), which, up through the Renaissance, labeled a revered house, such as a Domus Dei, or 'House of God', regardless of the shape of its roof. This is reflected in the uses of the Italian word duomo, the German/Icelandic/Danish word dom ('cathedral'), and the English word dome as late as 1656, when it meant a 'Town-House, Guild-Hall, State-House, and Meeting-House in a city.' The French word dosme came to acquire the meaning of a cupola vault, specifically, by 1660. This French definition gradually became the standard usage of the English dome in the eighteenth century as many of the most impressive Houses of God were built with monumental domes, and in response to the scientific need for more technical terms. A dome is a rounded vault made of either curved segments or a shell of revolution, meaning an arch rotated around its central vertical axis. The terminology used has been a source of controversy, with inconsistency between scholars and even within individual texts, but the term 'dome' may be considered a 'blanket-word to describe an hemispherical or similar spanning element.' A half-dome or semi-dome is a semi-circular shape often used, especially in apses. Sometimes called 'false' domes, corbel domes achieve their shape by extending each horizontal layer of stones inward slightly farther than the lower one until they meet at the top. A 'false' dome may also refer to a wooden dome. 'True' domes are said to be those whose structure is in a state of compression, with constituent elements of wedge-shaped voussoirs, the joints of which align with a central point. The validity of this is unclear, as domes built underground with corbelled stone layers are also in compression from the surrounding earth. The Italian use of the term finto, meaning 'false', can be traced back to the 17th century in the use of vaulting made of reed mats and gypsum mortar. As with arches, the 'springing' of a dome is the level from which the dome rises. The top of a dome is the 'crown'. The inner side of a dome is called the 'intrados' and the outer side is called the 'extrados'. The 'haunch' is the part of an arch that lies roughly halfway between the base and the top. The word 'cupola' is another word for 'dome', and is usually used for a small dome upon a roof or turret. 'Cupola' has also been used to describe the inner side of a dome. Drums, also called tholobates, are cylindrical or polygonal walls with or without windows that support a dome. A tambour or lantern is the equivalent structure over a dome's oculus, supporting a cupola.