Pope Francis said on Sunday (July 12) he was hurt by Turkey's decision to make Istanbul's Hagia Sophia museum a mosque.
"My thoughts go to Istanbul. I think of Santa Sophia and I am very pained."
He is the the latest religious leader to condemn the move.
A court ruling revoked the ancient monument's status as a museum.
Turkish President Tayyip Erdogan declared the Haiga Sophia was once again a mosque, and the first prayers would be held on July 24.
It's one of Istanbul's top tourist attractions, and lay at the heart of both the Christian Byzantine and Muslim Ottoman empires.
The World Council of Churches has called on Erdogan to reverse his decision.