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Photo: Sadrettin, CC BY-SA 4.0 via Wikimedia Commons
Built in the early 5th century as a monastery dedicated to Saint Andrew the Apostle, in 766 it was the burial place of Saint Andrew of Crete and was later re-dedicated to him. It was rebuilt in the late 9th century and again in the 13th, then around 1490 converted into a mosque. From the 16th century it was occupied by the Dervishes, when the legend arose that a chain hung to a cypress tree in the courtyard was a truth diviner. The chain was swung between rival witnesses and the one it hit was telling the truth. The cypress stump is still standing.
Koca Mustafa Pasha Mosque is a former Eastern Orthodox church converted into a mosque by the Ottomans, located in Istanbul, Turkey. The church, as the adjoining monastery, was dedicated to Saint Andrew of Crete, and was named Saint Andrew in Krisei or by-the-Judgment. Although heavily transformed during both the Byzantine and the Ottoman eras, it is one of the few extant churches in Istanbul whose foundation goes back to the sixth century.
© OpenStreetMap contributors
The Golden Gate was the ceremonial entrance through the Theodosian city walls. After the Ottomans captured the city in 1453, Mehmed II needed a stronghold for his treasures and documents. The gate was therefore bricked up and the walls reinforced into a fortress, with valuables stored in its seven towers, hence yedi kule. In the following century the treasury moved to Topkapi Palace and the fort became a prison for high-level detainees - Osman II was strangled here in 1622. It remained in use until 1837, whereupon the Golden Gate was re-opened.
This is a circular indoor space enclosed by a 3D depiction of the Ottomans breaching the Walls of Constantinople on 29 May 1453, with sound effects. It's over-priced, unhistorical and tourist-trappy.
The original mosque was built between 1463-1470 by the Greek architect Atik Sinan, by order of Sultan Mehmet II the Conqueror, on the site of the former Church of the Holy Apostles, which had served as Byzantine Imperial burial place for a thousand years. The grand complex with eight medreses, a library, hospital, hospice, caravanserai, market, hamam, primary school and public soup kitchen was smashed again and again by earthquakes, and the present building is from 1771 to a different design. The interior is lavish, and outside is the ornate tomb of Mehmet II and his wife Gülbahar Hatun.
This is a triple structure: the church of the Monastery of Pantokrator built 1118, then a public church circa 1136 plus a chapel that served as a royal mausoleum. It became a mosque and medresse in Ottoman times, but without massive alteration so it's a prime example of middle-Byzantine architecture. It's nowadays again a mosque, photogenic by day or dusk but the area should be avoided at night.
Imposing mosque built 1500/05. The other parts of the religious complex have found secular use.
Pammakaristos Church
The Church of Theotokos Pammakaristos ("All-Blessed Mother of God") was built between the 11th and 12th centuries. The parekklesion or side-chapel was added maybe 1300, with rich mosaics. The main building became a mosque in 1591, named for Sultan Murad III's conquest (fetih, hence Fethiye) of Georgia and Azerbaijan: the interior was opened up, but the chapel was undisturbed and in modern times became a museum. In 2020 the entire building was proclaimed a mosque, and every scrap of Byzantine artistry was covered up, so now there's nothing worth seeing.