Architectural Innovations of the Great Mosque of Córdoba
The Double-Arch System
The innovative system of overlapping arches was designed to provide greater elevation for the prayer hall. A column is placed on top of a pillar, approximately 2 meters high, from which the upper arch springs. This design incorporates Visigothic-style horseshoe arches at the bottom, which act as straps to prevent collapse, a significant improvement over the simple beams or braces used previously.
Horseshoe Arch Characteristics
The horseshoe arch features a camber of one-third of its radius, and its extrados (the outer curve) is not parallel to the intrados (the inner curve or soffit). An example of this style can be seen at the entrance of San Juan de Baños in Palencia.
The Impost Block and Corbel
Above the column’s capital, a unique impost block balances the thrusts from the arches. This cruciform ashlar (sillar) has projections at its ends. The longitudinal ridges serve as the first keystone for the arch, while the transverse section increases the pillar’s width. This element acts as a corbel and features a frontal decoration known as a roll cantilever. This decorative element is characteristic of Hispano-Moorish art and is considered a stylized evolution of the acanthus leaves found on Roman cornices.
Architectural Precedents
This system of overlapping arches was not entirely new, as similar structural solutions were used in earlier buildings, including:
- The Great Mosque of Damascus
- Al-Aqsa Mosque in Jerusalem
- The city of Anjar in Lebanon
- Early Christian and Byzantine basilicas
Bicolor Voussoirs and Roman Influences
The arches feature an alternation of materials in their voussoirs, using both stone ashlar and brick. This creates a striking visual effect of alternating red and white colors. This technique, which also helps manage material expansion and contraction, drew from existing Hispano-Roman tradition. Examples of this bicolor construction can be found in structures like:
- The Dome of the Rock in Jerusalem
- The Roman Aqueduct of the Miracles in Mérida
Structural Details and Roofing
The structure defies conventional approaches, as the supporting elements widen from 40 cm at the bottom to 1.10 m at the top. Each nave is covered by a gabled roof. Externally, the roof channels rainwater through pipelines, functioning like a small aqueduct. Internally, the prayer hall’s naves are covered by wooden roofs. The original floor was made of mortar and was typically covered with mats.
Aesthetic and Spatial Effects
This architectural system creates an extraordinary visual richness, evoking a labyrinthine “forest of columns.” It establishes a double directionality, and a more sophisticated perspective is achieved when viewing the columns crosswise. These artistic solutions connect to Byzantine, Umayyad-Syrian, and Hispano-Roman traditions.
Exterior Walls of the Original Mosque
Of the original exterior walls built by Abd-al Rahman I, only the west wall remains, as the others were removed during subsequent expansions. This wall is constructed from stone blocks arranged in stretchers and headers (a soga y tizón), a technique reflecting Umayyad, Visigothic, and Hispano-Roman traditions. The wall is divided into sections by aesthetic elements that serve no structural function and is crowned with characteristic staggered or toothed battlements, a common feature in the Umayyad world.
The Puerta de San Esteban (Bab al-Wuzara)
Several gates open onto the wall, with the Puerta de San Esteban being the best-preserved example. It was originally known as Bab al-Wuzara (Gate of the Viziers), as it was situated across the street from the Government House and was likely used by important officials. Although reformed in the 9th century and partially remodeled during the time of Muhammad I, it retains significant original elements.
This gate established the architectural model for facades built during later Emirate and Caliphate periods. It features a tripartite design with a superposition of floors. The central section, containing the main doorway, has three superimposed floors, while the two narrower side sections are simpler.