It has already been noted that the employment of the dome on pendentives over square bays led to the construction of churches with a broad nave without side aisles. Among the earliest of these are the church of Saint Astier (Dordogne), (founded about 1010 but so mutilated as to show little of its original construction),[18] and Saint Avit-Sénieur (Dordogne) (cir. 1117), originally with three domes which were replaced by domed up Anjou vaults in the thirteenth century.[19] The best of the earlier examples remaining for critical study are, first, the cathedral of Saint Pierre at Angoulême, whose western bay was constructed between 1100-1125,--the remaining three being but slightly later--and second, the church of Saint Étienne at Périgueux, originally with four domes, two of which were destroyed in the religious wars of the sixteenth century. Of the two which remain the more recent must be earlier than 1163, and the other would seem from its appearance to be about contemporary with that of the west bay of Angoulême.[20] These two with the cathedral of Saint Front (after 1120) furnish three excellent examples of the school, to which a large number of other churches might be added as illustrating some minor differences in plan or elevation.[21] The cathedral of Angoulême (Figs. 3 and 4) is characteristic of the school. Deep wall, and heavy transverse arches supply substantial impost for the domes. The piers of the western bay are of simple rectangular plan like those of Saint Avit-Sénieur and Saint Étienne at Périgueux, while those to the east are of a later compound type with transverse arches and wall-arches in two orders instead of the single order of the earlier bay. Except over the crossing, where there is a high circular drum forming a lantern, the domes are not pierced with windows around their base. This is due to the fact that they are covered on the exterior by a wooden roof.[22] It is more usual to find four small windows at the base of each dome as in Périgueux, Saint Front (Fig. 1).[23] The use of stone in the construction of the domes explains the small number of these windows compared to that in Byzantine architecture,[24] since the stability of the vault would be threatened by too many openings. Besides this, the fact that the churches of Perigord have no aisles, properly speaking, permitted sufficient light to enter through windows in the side walls. In fact it seems quite possible that the windows in the domes of the Perigord churches were used to afford resting places for the frame work of the centering even more than for light, a fact which would also seem to be true of the four recesses left in the masonry just above the cornice of the domes of Angoulême cathedral (Fig. 4). [Illustration: FIG. 3.--ANGOULÊME, CATHEDRAL.] THE CENTERING OF PERIGORD DOMES