A dome is a common structural element of architecture that resembles the hollow upper half of a sphere. Domes do not have to be perfectly spherical in cross-section, however; it is sufficient that they simply be curved surfaces.
A dome can be considered as an arch which has been rotated around its vertical axis. As such, domes have a great deal of structural strength. They can be constructed of ordinary masonry, held together by friction and compressive forces.
See also: Geodesic dome