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History of Windows
Windows played but a minor role in Egyptian houses. They were small and set high in the wall, more for ventilation than for light. However, the hypostyle halls of such large Egyptian temples as Karnak had clerestories at the top of the central aisle for lighting. Greek temples were lighted only through the door, and in houses the rooms opened on courtyards and needed no further light. The more complex imperial Roman buildings, like basilicas and baths, often had large lunettes under the vaults, perhaps subdivided by mullions. Windows, though still small, became more numerous in the clerestories of Early Christian basilicas and later in Byzantine architecture. A ring of such windows at the base of the dome in Hagia Sophia, Istanbul, bathes its interior in soft light. In all these styles, the windows were little more than holes in the wall. Thin slabs or grills of translucent alabaster might exclude rain, but in most cases the windows were left open. With the Romanesque style of the llth and 12th centuries in western Europe, moldings began to enframe the windows and thus add to their prominence.
The window came into its own in the Gothic style beginning in the late 12th century. Its great cathedrals were cages of glass and stone with windows replacing the wall from buttress to buttress or pier to pier. The glass was set in the center of the wall, and moldings or colon-nettes adorned the diagonal splay of the arches or jambs inside and out. Since the lead bars that held the small pieces of stained glass were weak, stone mullions were needed to subdivide the window and to support the patterns of tracery within the arch. Especially in the late Gothic, elaborate patterns were popular.
In houses, the size and location of windows were determined by the rooms they lighted. Vertical mullions and horizontal transoms subdivided the larger windows. During the earlier Middle Ages, shutters closed such windows, though panels of horn or wooden lattices may have been used. By the 15th century in northern Europe, glass began to appear in houses, usually only in the upper part of the window with shutters for the lower part.
Though smaller than the Gothic, windows in the Italian Renaissance of the 15th and 16th centuries remained of substantial size. They were evenly spaced and arranged to produce a symmetrical design. The jambs were often molded, or the window enframed with pilasters or engaged columns. Cornices or pediments were set above them. Such windows were features in the design of the building.
The sashes of Gothic and Renaissance windows were invariably casements. The first certain appearance of the double-hung sash occurred in England late in the 17th century, and it rapidly replaced casements thereafter. The panes were small in size because of the difficulty of procuring sheets of glass of uniform thickness. Hence many panes were needed for each window. As methods of glass production improved during the 18th and 19th centuries, the size of the panes increased, and the number per window declined. Thus a window of 1730 might have 18 or even 24 panes, while one of the same size in 1830 would have only 4. This trend ultimately led in the 20th century to the single pane picture window and even to the window wall. In this last case, although the windows are the building, they have lost the individual prominence of Gothic or Renaissance windows.