Native name: Yeralti Camii
Yeralti Mosque (known as the Ground Mosque) was the crypt of a former Byzantine fortress that was controlling the entrance of the Golden Horn, enemy ships were blocked from entering the Golden Horn by an anchored chain. The place was used by the Ottomans after the conquest of Constantinople as an ammunition store. Then in the period of Mahmut I (1730-54) the place was transformed into a mosque in 1757. The low-ceiling is supported by squat pillars. There are 54 symmetrical buttresses in the main area and they are arranged in six rows of nine, which create little compartments for private prayer. In a side area, there are the tombs of two Arab soldiers killed in the first Arab siege. The mosque has a limited view because of its low ceiling.
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