Clerestory

Historically, a clerestory formed 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.

In addition to architecture, clerestories have been used in transportation vehicles such as buses and trains to provide additional lighting, ventilation, or headroom.

History

Ancient world

Clerestories appear to originate in Egyptian temples, such as the Great Hypostyle Hall, 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. They appeared in Egypt at least as early as the Amarna Period. Minoan palaces in Crete such as Knossos employed lightwells in addition to clerestories.

According to the Hebrew Bible, Solomon's Temple featured clerestory windows made possible by the use of a tall, angled roof and a central ridgepole.

The clerestory was used in the Hellenistic architecture of classical antiquity. The Romans applied clerestories to basilicas of justice and to the basilica-like thermae and palaces.

Early Christian and Byzantine basilicas

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.

Romanesque period

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.

Initially, the nave of a large aisled and clerestoried church was of two levels: arcade and clerestory. During the Romanesque period, a third level was inserted between them, a gallery called the triforium or tribune. The triforium generally opens into space beneath the sloping roof of the aisle. This became a standard feature of later Romanesque and Gothic large abbey and cathedral churches. Sometimes another gallery set into the wall space above the triforium and below the clerestory. This feature is found in some late Romanesque and early Gothic buildings in France. Conversely, many major churches in southern France and Spain, such as Santiago de Compostela Cathedral, omitted the clerestory entirely, having just the arcade and tribune levels.

The oldest glass clerestory windows still in place are from the late eleventh century and are found in Augsburg Cathedral in Bavaria, Germany.

Gothic period

In smaller churches, clerestory windows may be trefoils or quatrefoils. In some Italian churches they are ocular. In most large churches, they are an important feature, both for beauty and for utility. The ribbed vaulting and flying buttresses of Gothic architecture concentrated the weight and thrust of the roof, freeing wall-space for larger clerestory fenestration. Generally, in Gothic masterpieces, the clerestory is divided into bays by the vaulting shafts that continue the same tall columns that form the arcade separating the aisles from the nave.

The tendency was for the clerestory level to become progressively taller and the size of the windows to get proportionally larger in relation to wall surface, emerging in works such as the Gothic architecture of Amiens Cathedral or Westminster Abbey, whose clerestories account for nearly a third of the height of the interior.