ملف:Sancaktar Hayrettin Mosque 6207.jpg

English: It dates probably to the end of the 14th century. Though Strolling through Istanbul refers to it as a (former) church, the Wikipedia claims that for its small size it probably was a martyrion or burial chapel. It is an irregular octagon with an apse oriented towards the east. The masonry uses alternate courses of brick and ashlar, giving to the exterior the polychromy typical of the Palaiologan period. Remnants of walls still present in the northwest and south sides before the restoration showed that the building was not isolated, but connected with other edifices. A minaret has also been added to the restored building. Restoration was necessary after the 1894 Istanbul earthquake, which had its epicentre under the Sea of Marmara, partially destroyed the mosque, which was restored only between 1973 and 1976.