window, in architecture, the casement or sash, fitted with glass, which closes an opening in the wall of a structure without excluding light and air. It may have a square, round, or pointed head; may be single, double, or grouped; in relation to the wall, it may be flush, recessed, or projected. A projected window is called a bay window if polygonal, a bow window if semicircular, an oriel if it has corbeled brick or stone supports. A mullioned window is divided by slender bars into panes; when the bars radiate from the center of a circular bar it is called a wheel. It takes the name of rose window when adorned with stained glass or figure design. The long, narrow window of the English Perpendicular Gothic church is called a lancet; a lunette fills a somewhat crescent-shaped space under a vaulted intersection high upon a wall. A fanlight, characteristic of the American Colonial style, is either a semicircular transom, usually over an entrance, or a small attic window (or often a pair flanking the chimney). A French window reaches the floor and has double casements opening as doors; originating in France in the late Renaissance, it was adopted throughout the Continent and in the Southern states in America. The double-hung sashes (sliding up and down within the frame), first used in Renaissance England, attained wide popularity. In Spain windows are frequently ornate, with stone framework, an elaborate head, and a decorative iron grille. In Indian and Byzantine windows a pierced slab of marble or alabaster often substitutes for glass. Muslims also used cement frames in which colored glass was set in brilliant arabesque forms. Carved and turned wood grilles are found in Syria and Egypt. In China and Japan, rice paper, protected by a sliding wooden shutter, often takes the place of glass. Shell, also used in China, was employed by the Romans, as were thin panes of marble, mica, and horn. In modern architecture the use of windows has greatly increased in dwellings and in the exterior walls of factories and commercial buildings.

wheel window: see rose window.

rose window, large, stone-traceried, circular window of medieval churches. Romanesque churches of both England and the Continent had made use of the wheel window—a circular window ornamented by shafts radiating from a small center circle; and from this prototype developed the elaborate rose windows. The latter, in their full development, flourished especially in France, where they appear in practically every important Gothic cathedral, either over the center portal of the west front or on at least one of the transept ends. Stained glass was usually placed in them. The early examples, as on the west facade of the cathedral at Chartres (12th-13th cent.), were filled with plate tracery, pierced from a stone slab. With the perfection of bar tracery, the typical rose, as in the cathedral at Reims (13th-14th cent.) and in Notre-Dame de Paris (12th-14th cent.), was filled with numerous radiating bars and intermediate bars, joining to form pointed arches at the outer edge. In the final or flamboyant period the bars were arranged in wavy curves and more intricate patterns. This rich and closely packed tracery, as in the fine transept window of St. Ouen at Rouen, suggests the design of an open rose.

Opening in the wall of a building for light and air, and sometimes for framing a view. Since early times, the openings have been filled with stone, wooden, or iron grilles, with panes of glass or other translucent material such as mica or, in East Asia, paper. A window in a vertically sliding frame is called a sash window: a single-hung sash has only one half that moves; in a double-hung sash, both parts slide. A casement window swings open on hinges attached to the upright side of the frame. Awning windows swing outward on hinges attached to the top of the frame; hopper windows swing inward on hinges attached to the bottom of the frame. Large, fixed (nonoperating) areas of glass are commonly called picture windows. A bay window (see oriel) is an exterior projection of a bay of a building that also forms an interior recess, providing better light and view than would a window flush with the building line. Seealso Diocletian window; rose window; shōji.

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In Gothic architecture, a decorated circular window, often glazed with stained glass, that first appeared in mid-12th-century cathedrals. It was used mainly at the western end of the nave and the ends of the transept. The bar tracery of a High Gothic rose window consisted of a series of radiating forms, each tipped by a pointed arch at the outside of the circle. The rose windows of Notre-Dame de Paris are particularly noteworthy. In later Flamboyant-style tracery, the radiating elements consisted of an intricate network of wavy, double-curved bars.

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Bay window in an upper story, supported from below by projecting corbels. Usually semihexagonal or rectangular in plan, oriels first became prevalent early in the 15th century. They were often placed over gateways or entrances to manor houses and public buildings of the late Gothic and Tudor periods. In cities of North Africa and the Middle East, the moucharaby is an oriel that uses grills or lattices in place of glass and shutters. Seealso brise-soleil.

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