VI. Particular forms of church building. 1. Double apses and double choirs. Mainly in Africa and Spain, we know a series of churches with two opposed apses beginning with Orlansville, already cited. In Africa, N. Duval’s detailed study of the series has demonstrated that the two apses are not contemporary. The erection of a second apse at the front inside or outside may have been due to the need to reverse the orientation of the churches originally facing west. It seems more often to have been related to the creation of a center of a martyrial cult inside the building, a center which elsewhere might be placed near the apse N Syria or in an annexed building. In Spain we know at present, in the S, four churches provided with apses apparently contemporary with the construction of the church. These churches, generally very small, show a common typology, with side entrances preceded by galleries parallel to the building. According to Th. Ulbert, the second apse would also have a martyrial function. The form with two opposed apses recurs twice in the Mozarabic period 10th c.. As well as those double apses we find, in both Africa and Spain, cases of double choirs, where the second center of worship was confined to a platform or enclosure near the front. The arrangement with two apses or two choirs generally supposed a circulation between the two centers of worship, ensured by an axial corridor Spain, Iunca in Tunisia or by a lateral protection of the whole central aisle Sbeitla in Tunisia. It was also connected with a rearrangement of the entrances to the church see above for Spain. In another part of the West Rhineland, N and E Gaul we see a series of churches with double apse or double presbytery in the Carolingian era, a tradition that would be maintained in the Romanesque period, esp. in Rhineland. We may ask ourselves whether, despite the absence of early Christian evidence in Gaul, a Western tradition does not exist. The role played by the opposed apse could also be entrusted to a lateral apse or an annexed building juxtaposed at right angles triconch martyrium of Tebessa in Algeria.