Hagia Irene Church or Saint Irene Church is a Greek Eastern Orthodox church located in Istanbul, Turkey. It was built by Byzantine emperor Constantine the Great at the end of his reign (337 AD). The church was reconstructed in the 6th century AD during the reign of Justinian I. The Hagia Irene today operates as a museum and concert hall and it was inscribed as a UNESCO World Heritage Site in 1985 as part of Historic Areas of Istanbul.