An oculus (; ) is a circular opening in the center of a
dome
A dome () 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 m ...
or in a wall. Originating in
classical architecture
Classical architecture typically refers to architecture consciously derived from the principles of Ancient Greek architecture, Greek and Ancient Roman architecture, Roman architecture of classical antiquity, or more specifically, from ''De archit ...
, it is a feature of
Byzantine
The Byzantine Empire, also known as the Eastern Roman Empire, was the continuation of the Roman Empire centred on Constantinople during late antiquity and the Middle Ages. Having survived the events that caused the fall of the Western Roman E ...
and
Neoclassical architecture
Neoclassical architecture, sometimes referred to as Classical Revival architecture, is an architectural style produced by the Neoclassicism, Neoclassical movement that began in the mid-18th century in Italy, France and Germany. It became one of t ...
.
A horizontal oculus in the center of a dome is also called opaion (; ).
Oeil-de-boeuf
An ''oeil-de-boeuf'' (; ), also ''œil de bœuf'' and sometimes anglicized as ''ox-eye window'', is a relatively small
elliptical window
A window is an opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazed or covered in some other transparent or translucent ma ...
, typically for an upper storey, and sometimes set in a roof slope as a
dormer
A dormer is a roofed structure, often containing a window, that projects vertically beyond the plane of a Roof pitch, pitched roof. A dormer window (also called ''dormer'') is a form of roof window.
Dormers are commonly used to increase the ...
, or above a door to let in
natural light. These are relatively small windows, traditionally oval. The term is increasingly used for circular windows (in which case it could also be called an oculus), but not for holes in domes or ceilings.
Windows of this type are commonly found in the grand architecture of
Baroque
The Baroque ( , , ) is a Western Style (visual arts), style of Baroque architecture, architecture, Baroque music, music, Baroque dance, dance, Baroque painting, painting, Baroque sculpture, sculpture, poetry, and other arts that flourished from ...
France
France, officially the French Republic, is a country located primarily in Western Europe. Overseas France, Its overseas regions and territories include French Guiana in South America, Saint Pierre and Miquelon in the Atlantic Ocean#North Atlan ...
. The term is also applied to similar round windows, such as those found in
Georgian architecture
Georgian architecture is the name given in most English-speaking countries to the set of architectural styles current between 1714 and 1830. It is named after the first four Monarchy of the United Kingdom, British monarchs of the House of Han ...
in Great Britain, and later
Greek Revival
Greek Revival architecture is a architectural style, style that began in the middle of the 18th century but which particularly flourished in the late 18th and early 19th centuries, predominantly in northern Europe, the United States, and Canada, ...
and
Colonial Revival
The Colonial Revival architectural style seeks to revive elements of American colonial architecture.
The beginnings of the Colonial Revival style are often attributed to the Centennial Exhibition of 1876, which reawakened Americans to the arch ...
styles in North America, so that must be considered part of the usage. The term initially applied to horizontal elliptical windows, but is also used for vertical ones.
The spread is not limited to