The first Muslim prayers in nearly 86 years were held at Istanbul’s historic Hagia Sophia.
President Recep Tayyip Erdogan unveiled a new plaque outside, naming it “The Hagia Sophia Grand Mosque” before Friday prayers and two weeks after a Turkish court ruled the building could be converted back into a mosque.
But opinion in Turkey and across the world has been divided.
Christian leaders earlier urged the president to reverse the decision.
The Hagia Sophia was built 1,500 years ago as an Orthodox Christian cathedral during the Byzantine Empire.
It was converted into a mosque in 1453 after the Ottomans conquered Constantinople and renamed the city Istanbul.
Mustafa Kemal Ataturk, the founder of modern Turkey, decreed it should become a museum and it opened as one in 1935.
It is visited by millions of tourists each year and President Erdogan has said the building will remain open to everyone.
Officials say Christian mosaics inside the building will be covered during prayer times and uncovered at other times.
This report was produced and edited by Al Jazeera NewsFeed’s Hassan Ghani.