Claire-voie (architecture)

In architecture, a clerestory (ˈklɪərstɔːri ; clear storey, also clearstory, clearstorey, or overstorey) is a high section of wall that contains windows above eye level. Its purpose is to admit light, fresh air, or both. Historically, clerestory denoted an upper level of a Roman basilica or of the nave of a Romanesque or Gothic church, the walls of which rise above the rooflines of the lower aisles and are pierced with windows. Similar structures have been used in transportation vehicles to provide additional lighting, ventilation, or headroom. The technology of the clerestory appears to originate in the temples of ancient Egypt. The term "clerestory" is applicable to Egyptian temples, where the lighting of the hall of columns was obtained over the stone roofs of the adjoining aisles, through gaps left in the vertical slabs of stone. Clerestory appeared in Egypt at least as early as the Amarna period. In the Minoan palaces of Crete such as Knossos, by contrast, lightwells were employed in addition to clerestories. According to Biblical accounts, the Hebrew temple built by King Solomon featured clerestory windows made possible by the use of a tall, angled roof and a central . The clerestory was used in the Hellenistic architecture of the later periods of ancient Greek civilization. The Romans applied clerestories to basilicas of justice and to the basilica-like bath-houses and palaces. Early Christian churches and some Byzantine churches, particularly in Italy, are based closely on the Roman basilica, and maintained the form of a central nave flanked by lower aisles on each side. The nave and aisles are separated by columns or piers, above which rises a wall pierced by clerestory windows. During the Romanesque period, many churches of the basilica form were constructed all over Europe. Many of these churches have wooden roofs with clerestories below them. Some Romanesque churches have barrel-vaulted ceilings with no clerestory. The development of the groin vault and ribbed vault made possible the insertion of clerestory windows.