Eski Imaret Mosque

The Eski Imaret Mosque (Turkish: Eski Imaret Camii) is a former Byzantine church converted into a mosque by the Ottomans. The church has traditionally been identified as belonging to the Monastery of Christ Pantepoptes (Greek: Μονή του Χριστού Παντεπόπτη), meaning "Christ the all-seeing". It is the only documented 11th-century church in Istanbul which survives intact, and represents a key monument of middle Byzantine architecture. Despite that, it remains among the least studied buildings in the city.

Source: Wikipedia (CC BY-SA 4.0) — https://en.wikipedia.org/wiki/Eski_Imaret_Mosque