The Haghia Eirene or Hagia Irene (Aya İrini Kilisesi) is a former Orthodox church and the first church built in Constantinople. It is also the only church that was not turned into a mosque after the Ottomans conquered Istanbul in 1453. The Haghia Eirene served as the church of the Patriarchate before the Hagia Sophia was completed in 537. Just like all other monuments in Istanbul, it suffered damages and multiple metamorphoses.
The Hagia Sophia stands on what is believed to be the oldest site of Christian worship in Istanbul. Roman Emperor Constantine I ordered the church in the 4th century, making it the first church built in Constantinople. After being burned down during the Nike revolt in 532, Emperor Justinian I had the church restored in 548. By then the Patriarchate had already moved to the Hagia Sophia, which was completed in 537. Restorations were again required in the 8th century after severe damages caused by an earthquake.
The church measures 100 by 32 meters, with a 15m wide and 35m high dome. Inside are some fascinating features. It still has its original atrium, five rows with built-in seats embracing the apse, and a great simple black cross on a gold background in the half-dome above the main narthex, which dates back from the Iconoclastic period when all figurative images were forbidden. These features didn’t survive in other Byzantine churches of Istanbul.