An aisle is a passage on the side of the nave in a basilica-plan church. It is narrower than the nave and is usually separated from it by a row of columns connected by an architrave (beam) or arches. The purpose of aisles is to enlarge the interior of a church beyond the nave. Thus a church may have a nave or a nave and two or four aisles, depending on the size of the community it serves.
The aisle roof is lower than that of the nave. In Syria, North Africa, and Europe it formed a lean-to, but in Egypt, it was usually flat. Egyptian basilicas, like those of other Eastern countries, show traces of windows in the aisles. Western basilicas have had aisle windows since the fifth century (Günter, 1968, pp. 39-42).
Characteristic of the Egyptian basilica, except on the north coast, are the niches (see below) let into the outer walls of the aisle, often in close sequence (Deichmann, 1937, p. 34). They are probably a relic of the older mud-brick building method, and they contribute to the often enormous strength of the walls.
- Deichmann, F. W. Grundrisstypen des Kirchenbaus in frühchristlicher und byzantinischer Zeit im Morgenlande. Halle, 1937.
- Günter, R. Wand, Fenster und Licht. Herford, 1968.
- Monneret de Villard, U. “La basilica cristiana in Egitto.” In Atti del IV congresso internazionale di archeologia cristiana, Vol. 1. Rome, 1940.
- Orlandos, A. K. Basilik», pp.154-205. Athens, 1952.