clerestory

Windowed wall of a room that rises higher than the surrounding roofs to light the interior space. In large buildings, where internal walls are far from the outermost walls, the clerestory provides daylight to spaces that otherwise would be dark and windowless. This device was used in Byzantine and early Christian architecture and most highly developed in Romanesque and Gothic cathedrals. As the nave rose much higher than the roofs of the side aisles, its walls could be pierced by a row of windows near the ceiling.

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