Built between 1824 and 1848 in the Turkish style of Istanbul mosques, the Muhammad Ali Mosque is one of the most impressive and spectacular in the Citadel. It is also known as the "Mosque of Albastro" due to the material used in the covering. The porticoed courtyard has a fountain for ablutions in the center and has a small square tower with a clock. The interior of the mosque is devoid of any human or divine representation due to an express prohibition of the Muslim religion. This has led artists to develop geometric decorative themes and various forms of arabesque calligraphy to reproduce the verses of the Koran on the walls. These scriptures are so elaborate that only specialists can read them.