Since 1935, Hagia Sofia, originally built as an orthodox Christian cathedral in the 5th century, has been a museum. This after having functioned as a mosque since the middle of the 15th century.

But now the World Heritage Site has once again become a mosque. This following a decision by the Turkish authorities.

Thousands of worshipers

Outside the massive building, thousands of Muslims gathered on Friday to attend the inaugural Friday prayer. Those who could not fit indoors spread out on the lawns outside.

There was also President Erdogan, who wore a mouth guard, attended the prayer. Several world leaders had been invited to the ceremony, mainly from Muslim countries.

International criticism

The decision to turn Hagia Sofia into a mosque has been interpreted by Turkish critics as a move by Erdogan to bolster its popularity among voters.

But even Christians around the world have reacted strongly to the decision. One of them is Pope Francis.

- I think of Hagia Sofia and am filled with pain, the Pope said on July 10 when the move was announced.

At the same time as the inauguration ceremony was held in Turkey, Greek churches flagged at half mast. This is to express their grief over what they consider to be an insult to the former Christian cathedral.