A favourite form of decoration was that formed by a multiplication of minute pendentives, called the honeycomb ornament, the whole surface, as well as the dome above, being covered with an agglomeration of minute niches, the effect of which is frequently compared to that of stalactites. This form of ornament was much used, particularly in the mosques and palaces of Spain. In Cairo domestic architecture has a distinctive character of its own. The houses have reception-rooms on the ground floor, furnished with the divans, carpets, and lamps usual in Oriental manner of life, while the upper floors, occupied by the women, have projecting balconies of lattice wood-work, which permit them to see without being seen, and form an agreeable and picturesque feature on the exterior. The richness and the progress of Arabic art at a period when architecture had sunk to the lowest ebb throughout Europe, is due in great measure to the establishment of the learned academies of Damascus, Bagdad, and other principal cities, and to the revival of Classic learning by the translation of the works of Greek authors. In Spain, where the Moorish and Christian populations were thrown in constant contact with one another, the difference of religious opinion maintained a wide gulf between them, and while the Christians struggled with the difficulties of the Romanesque revival, their opponents attained a brilliant era in art, as a result of their superior industry and civilization. One of the oldest Arabian buildings in Spain is the great mosque at Cordova. Here, as in the East, we find Corinthian and Composite columns, taken from Roman buildings on the soil, forming integral parts of the new structure, but the Classical principles of building are in no sense adhered to. The entablature is replaced by cinque-foiled arches with voussoirs of alternate stone and brick; a second order of columns is superposed directly upon the capitals of the first, carrying horseshoe arches, and between the two arcades an intermediary series of trefoiled arches is placed, springing from the keystone of the lower arches and divided at the centre by the upper ones. The general plan of the building consists of the usual series of aisles, of which there are nineteen, with divisional walls. The sanctuary has a vault with intersecting ribs, surmounted by a small dome and enriched by profuse ornament, and is the object of much just admiration for its beauty. The chapel of Villa Viciosa, a later structure, has a series of arcades similar to those before the sanctuary, differing only in the arrangement of the intermediary arches, which are carried up to the level of the upper arches from a horizontal course, and are cinque-foiled instead of trefoiled, both on the extrados and intrados.