St Peter's Basilica, Rome

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 saucer dome is a dome section of large radius that caps a space with a low dome. A variant is the Onion dome that resembles more than half of a sphere, exemplified by Saint Basil's Cathedral in Moscow.

The concave triangular sections of vaulting that provides the transition between a dome and the square base on which it is set and transfer the weight of the dome are called pendentives. A less sophisticated version of a pendentive is a squinch..

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.

A half-dome forms the head of an exedra or its smaller version, a niche. In Late Antiquity, the exedra developed into the apse, with separate developments in Romanesque and Byzantine practice.

Famous domes

Listed in order of their completion:

• The Pantheon in Rome;
• The domes and half-domes of Hagia Sophia in Constantinople;
• The Dome of the Rock in Jerusalem;
• Filippo Brunelleschi's dome of the Duomo in Florence;
• Bramante's dome of the "Tempietto" in Rome;
• The dome of St. Peter's Basilica in Rome;
• The Blue Mosque in Istanbul;
• The Taj Mahal in Agra;
• The dome of Les Invalides in Paris;
• Wren's dome of St Paul's Cathedral in London;
• James Gibb's dome at the Radcliffe Camera in Oxford;
• The steel-framed (http://www.aoc.gov/) United States Capitol dome, Washington, DC;
• The Millennium Dome in London.

See also

• Geodesic dome
• Cupola
• Concrete dome