Now used as a museum, Hagia Sophia was once a patriarchal basilica which was later converted into a mosque. Built sometime around 532 AD, Hagia Sophia was the largest cathedral in the world for nearly a thousand before Seville Cathedral was built in the year 1520. The mosque is a brilliant piece of Byzantine architecture and is thought to be this architectural style's best preserved example. There are four minarets surrounding the former mosque, one of which is build of red brick where as the other three are built from white marble. At night, the mosque is partially illuminated which makes for a pleasant sight. The view of interiors of Hagia Sophia will simply leave you mesmerized. One can easily see the many Islamic features that adorn the dome and the walls. The museum houses many private belongings of the Sultan, and numerous manuscripts.