Eski Imaret Mosque
Istanbul, Turkey · built 1001
The Eski Imaret Mosque (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, 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.
Mosque data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).