During the eighth century, the Umayyad Caliphate reached as far east as India and as far west as Spain and Portugal, a region known in Arabic as al-Andalus. The city of Córdoba was the capital of al-Andalus, and was home to one of the most impressive examples of mosque architecture in the Islamic world. The Great Mosque of Córdoba was one of the largest mosques ever built. It has no central altar or shrine, but features a prayer hall that reaches over 250,000 square feet. Besides its large size, the Great Mosque’s prayer hall is notable for its use of hypostyle, creating the effect of a forest of columns that supports double rows of horseshoe-shaped arches made up of red and white bricks, called voussoirs. As a result, the Great Mosque’s hypostyle hall feels immensely large. Artists and architects continued to work on the Great Mosque for over two hundred years after its initial construction, adding geometric marble carvings, grand mosaics, public fountains, and gardens. After Spain was conquered by Christians in the fifteenth century, the Great Mosque was converted into a cathedral.