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The Eyüp Sultan Camii  is one of the most holy and important mosques in all of Turkey. It is so revered because it located on the site of the tomb of ABU AYYUP ALANSARI  (Eyüp Ensari in Turkish) – who was both a friend and standard bearer for the Prophet Muhammed, and was killed during the first Arab siege of Constantinople (674-678).
Eyup Sultan Mosque history
The mosque was erected on the instruction of Fatih Sultan Mehmet II (aka Mehmet The Conqueror), five years after he seized Constantinople for the Ottomans in 1453. However it fell into disrepair and was further ruined by earthquakes. It was rebuilt in a Baroque style using attractive pale honey-colored stone in 1800. The interior is elegant in design and the decorated dome of Eyup Sultan Mosque measures 17.5m in diameter and is supported by two half domes. 
The tomb of Eyüp is perhaps more interesting than the mosque itself.  Open Tuesday-Sunday from 9:30am-4:30pm, it is covered in tile panels from a number of different periods, which create a beautiful, if overwhelming effect.
The Eyüp Cemetery, which leads up the hill from the mosque, is a pleasant leafy area to stroll through. At the top is the Pierre Loti Café, where you enjoy a Turkish tea or coffee with stunning views out across the Golden Horn (best enjoyed at sunset). The café is named after the French novelist and Turkophile who used to come here for inspiration.