In passing now to a consideration of the distinct forms developed from these pre-Byzantine types of church building, the classification adopted by Professor Strzygowski may be followed. In his Kleinasien he has brought forward a series of buildings which show the manner in which a dome was fitted to the oblong basilica, producing the domed basilica (Küppelbasilica), an evolution which he regards as Hellenistic and Eastern. In contrast to this, Strzygowski distinguishes the domed cross church (Kreutzküppelkirche), of which S. Theodosia in Constantinople (p. [170]) is the typical example and which is a Western development. A comparison of the two forms is of great importance for the study of certain Constantinople churches.
Fig. 1.—Kasr Ibn Wardan (Strzygowski).
The domed basilica, as the name indicates, is a basilica with nave and aisles, in which a square bay in the centre of the nave is covered by a dome on pendentives. To north and south, within the arches supporting the dome, appear the nave and gallery arcades of the basilica; and as the galleried basilica is a usual Eastern form galleries are usual in the domed basilica. As seen from the central area, therefore, the north and south dome arches are filled in with arcades in two stories, and the side aisles and galleries are covered with barrel vaults running parallel to the axis of the church. At the west end a gallery over the narthex may unite the two side galleries. At Kasr ibn Wardan, instanced by Strzygowski as a typical domed basilica,[15] there is such a western gallery (Fig. [1]). According to Strzygowski the domed basilica is older than the fifth century.
The domed basilica remains always an oblong building, and whilst the two sides to north and south are symmetrical, the western end retains the basilican characteristics—it has no gallery or arcade communicating with the central area. The narthex communicates with the nave by doors, and if a gallery is placed above it, both narthex and gallery are covered by barrel vaults.
In the domed cross church (Kreutzküppelkirche) the central dome rests on barrel vaults which extend to the outer walls of the building and form the arms of the cross, the eastern arm forming the bema. The lighting of the church is by windows in the gable walls which terminate the north, south, and west cross arms. The prothesis and diaconicon open off the side arms, and two small chambers in the western angles of the cross bring the plan externally to the usual rectangular form.
The domed cross church may have galleries, as in S. Theodosia (p. [170]), or may be without them, as in SS. Peter and Mark (p. [193]). Where galleries are present they are placed in the cross arms and are supported by arcades at the ground level. The vaults beneath the galleries are cross-groined. The domed cross church is a centrally planned church, in contrast to the domed basilica, which is oblong, and therefore we should expect that where galleries are used they will be formed in all three arms of the cross, as is the case in S. Theodosia.
There are a number of churches which vary from these types, but which can generally be placed in one class or the other by the consideration of two main characteristics: if the dome arches extend to the outer walls the building is a domed cross church; if the galleries are screened off from the central area by arcades the building is a domed basilica.