“The sea takes my thought a bit far, to Istanbul,” Pope Francis said at his weekly Angelus prayer on Sunday. “I think of Hagia Sophia, and I am very saddened.”

He stood in silence for several minutes after talking about Turkey’s decision to convert the Hagia Sophia cathedral back into a mosque.

The UNESCO World Heritage Site has served as a museum since 1934, but on Friday the decades-long cabinet decree was annulled by a Turkish court. Turkish President Recep Tayyip Erdogan issued a presidential decree to transfer the management of the building from the Turkish Ministry of Culture to the country’s Presidency of Religious Affairs.

The iconic cathedral was constructed in the 6th century. After the sacking of Constantinople by the Ottomans in 1453 it became a mosque.

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Since Islam forbids images of people to be displayed in mosques, the mosaics and icons had been covered by plaster before restoration works revealed them again once the cathedral was used as a museum. This time, the numerous Byzantine Christian mosaics in the Hagia Sophia will be covered by lights and curtains, said Ali Erbas, Turkey’s head of religious affairs during an interview on Turkish TV. He said that the mosaics would be covered during services but will then be uncovered for visitors wishing to marvel the works.

President Erdogan said that the entrance fees would be cancelled once the conversion was complete. “Like all our mosques, its doors would be open to everyone, Muslim or non-Muslim,” he said.