The intersection of the nave and transept was usually treated by the Romanesque builders as a distinctive vaulting bay. Occasionally, in the tunnel-vaulted churches, the builders allowed the vault of nave and transept to intersect and form a groined vault at the crossing, as, for example, in Saint Étienne at Beaugency (after 1050) (Loiret)[305] and in the church of Boisney (Eure).[306] Groined vaults are also found in this position in certain churches, like those of the Rhenish provinces, where similar vaults are used in the nave. But as a general rule, the crossing of the Romanesque church is covered by a dome resting on spherical pendentives or squinches, either unraised or else placed on a drum, which thus forms a lantern with windows to light the church interior. There is no necessity for an extended discussion of raised and unraised domes, since as far as construction is concerned they differ only in the fact that when raised on a lantern they are somewhat more difficult to support because the vaults of choir, nave, and transept no longer serve as buttressing members. The custom, however, of erecting a tower even above the raised domes offset to a large extent the thrusts which they created. Sometimes these Romanesque crossing domes are of circular plan and supported on spherical pendentives. These are common in the school of Perigord, where examples are afforded by the cathedral of Périgueux (Fig. 1) or the abbey church of Solignac.[307] But the use of such domes on spherical pendentives was not confined to Perigord. They are found in Poitou and Les Charentes, in the Southwest, and even in Limousin.[308] One of the best examples, and one in which there is a circular drum below the dome, appears in the church of Le Dorat (cir. middle twelfth century) (Haute-Vienne).[309] Very occasionally, also, the flat triangular pendentive is used, as in Notre Dame at Chauvigny (Vienne).[310] LANTERN TOWERS