Professor Strzygowski gives examples of cross-planned cells in the catacombs of Palmyra,[13] and in many Eastern rock tombs.[14] Such cross plans are found also in the Roman catacombs. These subterranean chapels, of course, do not show the external treatment, yet there can be little doubt that the external cross plan was originally sepulchral, and owes its peculiar system of planning to that fact. On the other hand, it was adopted in such churches as S. Mark's at Venice and in the French examples of Périgord for aesthetic or traditional reasons. 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 (_Kuppelbasilica_), an evolution which he regards as Hellenistic and Eastern. In contrast to this, Strzygowski distinguishes the domed cross church (_Kreuzkuppelkirche_), 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. [Illustration: 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.