Spain (Andalucia): Cordoba: the Mesquita: Photo 9
The columns support double-decked arches--the upper circular, the lower slightly horseshoe-shaped. It's a design adapted from Roman aqueducts such as the one at Merida, which also alternates brick and stone voussoirs in a pattern called ablaq in Arabic. The horseshoe arch, so associated with the Moors, was also an adopted form, in its case taken from the Visigoths, who had used it in churches such as San Juan de Banos, built in Palencia about 660.