The Mezquita, or Great Mosque of Cordoba, was the third largest mosque in the world.  The mosque, a conglomerate building incorporating Roman, Gothic, Byzantine, Persian, and Syrian elements in its architecture, was started by Caliph Abderraman I in the early 9th century C.E., and construction continued under his successors until 1236 C.E., when Cordoba was reconquered by Christian forces who remodeled the building into a cathedral. Oddly, the edifice didn't point towards Mecca as was the norm, but faced Abderraman I's hometown of Damascus. Even more impressive than the architecture was the learning that took place in the Mezquita. Muslims were known throughout the Medieval world for their knowledge, and this mosque was a center for the learning of poetry, calligraphy, astronomy, politics and history, the life sciences, and philosophy as well as Islamic religious training. Scholars from around the Muslim world - and beyond - flocked to the Great Mosque in the hopes of furthering their education. Of course, with the decline of Islamic power and the rise of the European university, the building (now a Renaissance cathedral) ceased to be anything but a religious monument - albeit a beautiful one.