As we were enjoying the beautiful blue tiles of Rustum Pasa mosque, a look outside revealed clearly this was a former Byzantine church, now converted to a mosque. In books like 'churches of Istanbul' it lists numerous churches but only when one examines it further that one realises that most of them have been converted to mosques or have been destroyed and sitting on top is a new mosque. Even with these converted mosque a lot of them are not in the best condition. It takes a lot of money to maintain these old former Byzantine buildings. During the Ottoman decades the religious mosaics have been whitewashed over like in the case of Haghia Sophia and the Kariye muzesi. Recently the whitewash has been removed and cleaned off to reveal the Byzantine mosaics and frescoes.