An oculus (from Latin oculus 'eye'; pl. oculi) is a circular opening in the center of a dome or in a wall. Originating in classical architecture, it is a feature of Byzantine and Neoclassical architecture.
A horizontal oculus in the center of a dome is also called opaion (from Ancient Greek ὀπαῖον (opaîon) '(smoke) hole'; pl. opaia).
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The megaron (/ˈmɛɡəˌrɒn/; Ancient Greek: μέγαρον, [mégaron], pl.: megara /ˈmɛɡərə/) was the great hall in very early Mycenean and ancient Greek palace complexes. Architecturally, it was a rectangular hall that was supported by four columns, fronted by an open, two-columned portico, and had a central, open hearth that vented though an oculus in the roof.
The megaron also contained the throne-room of the wanax, or Mycenaean ruler, whose throne was located in the main room with the central hearth. Similar architecture is found in the Ancient Near East, though the presence of the open portico, generally supported by columns, is particular to the Aegean. Megara are sometimes referred to as "long-rooms", as defined by their rectangular (non-square) shape and the position of their entrances, which are always along the shorter wall so that the depth of the space is larger than the width. There were often many rooms around the central megaron, such as archive rooms, offices, oil-press rooms, workshops, potteries, shrines, corridors, armories, and storerooms for such goods as wine, oil, and wheat. Evidence suggests that the megara of ancient Greece were often created using the construction techniques of wattle-and-daub and pisé.
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.
Rose window is often used as a generic term applied to a circular window, but is especially used for those found in Gothic cathedrals and churches. The windows are divided into segments by stone mullions and tracery. The term rose window was not used before the 17th century and comes from the English flower name rose.
The name "wheel window" is often applied to a window divided by simple spokes radiating from a central boss or opening, while the term "rose window" is reserved for those windows, sometimes of a highly complex design, which can be seen to bear similarity to a multi-petalled rose. Rose windows are also called "Catherine windows" after Saint Catherine of Alexandria, who was sentenced to be executed on a spiked breaking wheel. A circular window without tracery such as are found in many Italian churches, is referred to as an ocular window or oculus.
Domes were a characteristic element of the architecture of Ancient Rome and of its medieval continuation, the Byzantine Empire. They had widespread influence on contemporary and later styles, from Russian and Ottoman architecture to the Italian Renaissance and modern revivals. The domes were customarily hemispherical, although octagonal and segmented shapes are also known, and they developed in form, use, and structure over the centuries. Early examples rested directly on the rotunda walls of round rooms and featured a central oculus for ventilation and light. Pendentives became common in the Byzantine period, provided support for domes over square spaces.
Early wooden domes are known only from a literary source, but the use of wooden formwork, concrete, and unskilled labor enabled domes of monumental size in the late Republic and early Imperial period, such as the so-called "Temple of Mercury" bath hall at Baiae. Nero introduced the dome into Roman palace architecture in the 1st century and such rooms served as state banqueting halls, audience rooms, or throne rooms. The Pantheon's dome, the largest and most famous example, was built of concrete in the 2nd century and may have served as an audience hall for Hadrian. Imperial mausolea, such as the Mausoleum of Diocletian, were domed beginning in the 3rd century. Some smaller domes were built with a technique of using ceramic tubes in place of a wooden centering for concrete, or as a permanent structure embedded in the concrete, but light brick became the preferred building material over the course of the 4th and 5th centuries. Brick ribs allowed for a thinner structure and facilitated the use of windows in the supporting walls, replacing the need for an oculus as a light source.
The United States Capitol features a dome situated above its rotunda. The dome is 288 feet (88 m) in height and 96 feet (29 m) in diameter. Designed by Thomas U. Walter, the fourth Architect of the Capitol, it was constructed between 1855 and 1866 at a cost of $1,047,291 (equivalent to $17.6 million in 2024). The Statue of Freedom tops the lantern on the dome, and the dome is centered over the origin on street maps of Washington, D.C.
The dome is not stone, but rather cast iron carefully painted to appear to be made of the same stone as the capitol building below. It is actually two domes, one inside the other, and the total weight is 9.1 million pounds (4,100 t). The dome's cast iron frame was supplied and constructed by the iron foundry Janes, Fowler, Kirtland & Co. in the Bronx, New York. The interior of the dome includes a detailed geometric and floral pattern of lightly colored plasterwork, with Constantino Brumidi's monumental ceiling fresco, The Apotheosis of Washington, appearing in the oculus at the top of the inner dome.
Illusionistic ceiling painting, which includes the techniques of perspective di sotto in sù and quadratura, is the tradition in Renaissance, Baroque and Rococo art in which trompe-l'œil, perspective tools such as foreshortening, and other spatial effects are used to create the illusion of three-dimensional space on an otherwise two-dimensional or mostly flat ceiling surface above the viewer. It is frequently used to create the illusion of an open sky, such as with the oculus in Andrea Mantegna's Camera degli Sposi, or the illusion of an architectural space such as the cupola, one of Andrea Pozzo's frescoes in Sant'Ignazio, Rome. Illusionistic ceiling painting belongs to the general class of illusionism in art, designed to create accurate representations of reality.
A skylight (sometimes called a rooflight) is a light-permitting structure or window, usually made of transparent or translucent glass, that forms all or part of the roof space of a building for daylighting and ventilation purposes.