60 second video inside of mosque in Cordoba spain , The most important building and symbol of the city, the Great Mosque of Córdoba is now a christian cathedral, kzbin.info/www/bejne/fYiQfX2KaZKmr6c . see wiki '' It has been estimated that in the 10th century Córdoba was the most populous city in the world,[3] and under the rule of Caliph Al Hakam II it had also become a centre for education under its Islamic rulers. Al Hakam II opened many libraries in addition to the many medical schools and universities which existed at this time. During these centuries Córdoba became a predominantly Muslim society .