The Hagia Sophia Grand Mosque/Ayasofya-i Kebir Cami-i Şerifi, with its innovative architecture, rich history, religious significance and extraordinary characteristics has been fighting against time for centuries, was the largest Eastern Roman Church in Istanbul. Constructed three times in the same location, it is the world’s oldest cathedral. From 1935 until 2020 it was officially a museum, but has again become a functioning mosque.