geodesic dome, structure that roughly approximates a hemisphere. Popular in recent years as economical, easily erected buildings, geodesic domes are geometrically determined from a model and may be constructed from limited materials. The architect Buckminster Fuller was an early proponent of geodesics for housing and other functions. Among the best-known examples of geodesic domes have been the United States Pavilion at Montreal's Expo 67 and Biosphere II, an experimental recreation of the ecosystem in Arizona.

dome, a roof circular or (rarely) elliptical in plan and usually hemispherical in form, placed over a circular, square, oblong, or polygonal space. Domes have been built with a wide variety of outlines and of various materials.

Early Domes

The earliest domes were probably roofed primitive huts and consisted of bent-over branches plastered with mud. Another primitive form, called a beehive dome, is constructed of concentric rings of corbeled stones and has a conical shape. Ancient examples have been found in the tombs of Mycenae and can also still be seen in the folk architecture of Sicily. Although there is evidence of widespread knowledge of the dome, its early use was apparently restricted to small structures built of mud brick.

Roman and Byzantine Domes

It was the Romans who first fully realized the architectural potentialities of the dome. The Roman development in dome construction culminated in the pantheon (2d cent. A.D.). The Romans, however, failed to discover a proper handling of the pendentive—the device essential to placing a dome over a square compartment—that was finally achieved by the Byzantine builders of Hagia Sophia at Constantinople (A.D. 532-37). The other solution to placing a dome over a square was the squinch, which in the form of stalactites was to receive superb expression in Islamic architecture. Under Byzantine influence the Muslims early adopted the use of the dome; one of their first important monuments is the Dome of the Rock in Jerusalem. They often used the so-called Persian or onion dome. The most celebrated example is the Taj Mahal (A.D. 1630) at Agra, India.

Renaissance Refinements

Both the influence of the Roman Pantheon and of the Byzantine pendentive came to bear on the designers of the Italian Renaissance, and the crossings of many churches of the period were covered by masonry domes on pendentives. Between pendentive and dome a circular drum usually was interposed, serving to give greater elevation and external importance as well as a space for the introduction of windows. By the addition of an outer shell, the exterior came to be independently designed for maximum effectiveness, and the placing of a lantern at the top of this outer shell provided an apex for the entire composition.

Modern Domes

The dome in modern architecture utilizes such materials of construction as reinforced and thin-shell concrete, glass and steel, and plastic. An innovative contemporary approach to the form is the geodesic dome. These are low-cost, geometrically determined hemispherical forms as promoted by architect Buckminster Fuller.

Outstanding Domes

Celebrated examples are Brunelleschi's octagonal ribbed dome for the Cathedral of Florence (1420-36); St. Peter's, Rome, designed by Michelangelo, with two masonry shells (completed 1590), internal diameter 137 ft (42 m); the church of the Invalides, Paris, by J. H. Mansart (1706), 90 ft (27 m); St. Paul's Cathedral, London, by Sir Christopher Wren (1675-1710), 112 ft (34 m); and the Panthéon, Paris, by J. G. Soufflot (1775-81), 69 ft (21 m). The last three domes are built with triple shells, the middle shells serving to support the crowning lanterns.

In the United States the dome of the Massachusetts state capitol, designed (1795) by Charles Bulfinch, established the dome as a distinctive feature for numerous later state capitols as well as for the national Capitol at Washington, D. C. The dome of the latter, however, is of cast iron instead of masonry. The design, by T. U. Walter, has an inner diameter of 90 ft (27 m) and possesses great external impressiveness.

Teapot Dome, in U.S. history, oil reserve scandal that began during the administration of President Harding. In 1921, by executive order of the President, control of naval oil reserves at Teapot Dome, Wyo., and at Elk Hills, Calif., was transferred from the Navy Dept. to the Dept. of the Interior. The oil reserves had been set aside for the navy by President Wilson. In 1922, Albert B. Fall, U.S. Secretary of the Interior, leased, without competitive bidding, the Teapot Dome fields to Harry F. Sinclair, an oil operator, and the field at Elk Hills, Calif., to Edward L. Doheny. These transactions became (1922-23) the subject of a Senate investigation conducted by Sen. Thomas J. Walsh. It was found that in 1921, Doheny had lent Fall $100,000, interest-free, and that upon Fall's retirement as Secretary of the Interior (Mar., 1923) Sinclair also "loaned" him a large amount of money. The investigation led to criminal prosecutions. Fall was indicted for conspiracy and for accepting bribes. Convicted of the latter charge, he was sentenced to a year in prison and fined $100,000. In another trial for bribery Doheny and Sinclair were acquitted, although Sinclair was subsequently sentenced to prison for contempt of the Senate and for employing detectives to shadow members of the jury in his case. The oil fields were restored to the U.S. government through a Supreme Court decision in 1927.

Dome of the Rock: see Islamic art and architecture.

Clingmans Dome, mountain, Tenn.: see Great Smoky Mountains.

Largely subsurface geologic structure that consists of a vertical cylinder of salt embedded in horizontal or inclined strata. In the broadest sense, the term includes both the core of salt and the strata that surround and are “domed” by the core. Major accumulations of oil and natural gas are associated with salt domes in the U.S., Mexico, the North Sea, Germany, and Romania; domes along the Gulf Coast contain large quantities of sulfur. Salt domes are also major sources of salt and potash on the Gulf Coast and in Germany, and they have been used for underground storage of liquefied propane gas. Storage “bottles,” made by drilling into the salt and then forming a cavity by subsequent solution, have been considered as sites for disposal of radioactive wastes.

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In architecture, a hemispherical structure evolved from the arch, forming a ceiling or roof. Domes first appeared on round huts and tombs in the ancient Middle East, India, and the Mediterranean in forms, such as solid mounds, adaptable only to the smallest buildings. The Romans introduced the large-scale masonry hemisphere. A dome exerts thrust all around its perimeter, and the earliest monumental examples (see Pantheon) required heavy supporting walls. Byzantine architects invented a technique for raising domes on piers, making the transition from a cubic base to the hemisphere by four pendentives. Bulbous or pointed domes were widely used in Islamic architecture. The design spread to Russia, where it gained great popularity in the form of the onion dome, a pointed, domelike roof structure. The modern geodesic dome, developed by R. Buckminster Fuller, is fabricated of lightweight triangular framing that distributes stresses within the structure itself.

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or Mosque of Omar

Oldest existing Islamic monument. It is located on Temple Mount, previously the site of the Temple of Jerusalem. The rock over which it is built is sacred to both Muslims and Jews. In Islam, Muhammad is believed to have ascended into heaven from the site. In Judaism it is the site where Abraham prepared to sacrifice his son Isaac. Built in 685–91 as a place of pilgrimage, the octagonal building has richly decorated walls and a gold-overlaid dome mounted above a circle of piers and columns.

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