Mosque of Cordoba

The Mosque of Cordoba, in Andalucia, Spain was originally the site of a church which was bought by the Muslim Emir Abd ar-Rehman I and subsequently converted into one of the largest mosques in the world with work starting in 784 CE. Cordoba became one of the most advanced cities in the world, as well as a great cultural, political and economic centre and the mosque featured as a great centre of learning.

The building is most notable for its giant arches, with over 1,000 columns of jasper, onyx, marble, and granite; the double arches, which were a new architectural feature and the rich and exquisite design patterns making it one of the most beautiful mosques to have existed.

In 1236 CE, Cordoba was recaptured from the Muslims by King Ferdinand III and the mosque was reconsecrated as a Christian church, with the most significant alteration being the construction of a Renaissance cathedral nave in the middle of the structure (see above).

Reference:  Wikipedia