Dome

A dome (from Latin domus) is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a matter of controversy and there are a wide variety of forms and specialized terms to describe them.

A dome can rest directly upon a rotunda wall, a drum, or a system of squinches or pendentives used to accommodate the transition in shape from a rectangular or square space to the round or polygonal base of the dome. The dome's apex may be closed or may be open in the form of an oculus, which may itself be covered with a roof lantern and cupola.

Domes have a long architectural lineage that extends back into prehistory. Domes were built in ancient Mesopotamia, and they have been found in Persian, Hellenistic, Roman, and Chinese architecture in the ancient world, as well as among a number of indigenous building traditions throughout the world. Dome structures were common in both Byzantine architecture and Sasanian architecture, which influenced that of the rest of Europe and Islam in the Middle Ages. The domes of European Renaissance architecture spread from Italy in the early modern period, while domes were frequently employed in Ottoman architecture at the same time. Baroque and Neoclassical architecture took inspiration from Roman domes.

Advancements in mathematics, materials, and production techniques resulted in new dome types. Domes have been constructed over the centuries from mud, snow, stone, wood, brick, concrete, metal, glass, and plastic. The symbolism associated with domes includes mortuary, celestial, and governmental traditions that have likewise altered over time. 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.

Across the ancient world, curved-roof structures that would today be called domes had a number of different names reflecting a variety of shapes, traditions, and symbolic associations. The shapes were derived from traditions of pre-historic shelters made from various impermanent pliable materials and were only later reproduced as vaulting in more durable materials. The hemispherical shape often associated with domes today derives from Greek geometry and Roman standardization, but other shapes persisted, including a pointed and bulbous tradition inherited by some early Islamic mosques.

Modern academic study of the topic has been controversial and confused by inconsistent definitions, such as those for cloister vaults and domical vaults. Dictionary definitions of the term "dome" are often general and imprecise. Generally-speaking, it "is non-specific, a blanket-word to describe an hemispherical or similar spanning element." Published definitions include: hemispherical roofs alone; revolved arches; and vaults on a circular base alone, circular or polygonal base, circular, elliptical, or polygonal base, or an undefined area. Definitions specifying vertical sections include: semicircular, pointed, or bulbous; semicircular, segmental or pointed; semicircular, segmental, pointed, or bulbous; semicircular, segmental, elliptical, or bulbous; and high profile, hemispherical, or flattened. Domes with a circular base are called "circular domes", regardless of the shape of their cross-section.

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. 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. "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 in compression from the surrounding earth.