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One advantage in the employment of the dome of stone lay in the fact that it might be faced on both the exterior and the interior, or covered directly by tiles without the use of a bonnet of wood and copper, or a roof of wood and tile, so frequently seen in Byzantine work. It is doubtful whether the earliest French domes were treated in this way, however, for indications would seem to point to the original employment of a wooden roof over the domes of the cathedral of Saint Front.[16] Nevertheless, these domes have since been restored with an exterior stone facing (Fig. 2), and a similar treatment is to be seen at Cahors cathedral, and over

Fig. 2.—Périgueux, Cathedral.

the crossing of Angoulême. In these domes the drum is first built up in a slightly ramping wall, to offset the outward thrust of the vault, and the dome itself is crowned by a lantern toward which it has an upward curve, rendering the exterior steep enough to shed water readily. At Angoulême the domes of the nave are entirely concealed by a gable roof, perhaps in the early manner of the school. Still another type of dome covering appears at Saint Étienne in Périgueux,[17] where the curve of the dome does not show on the exterior, but where the drum is first carried up around the haunch, and then surmounted by a flattened conical roof of tile, which rests directly upon the vault beneath.