Thousands gathered around Istanbul's Hagia Sophia on Friday, as the historic building opened for Friday prayers and its conversion into a mosque became complete. Inside, President Erdoğan and ministers from the Turkish government knelt down at the beginning of a ceremony which marked the return of Muslim worship to the site. Meanwhile, crowds of worshippers congregated outside on prayer mats in Sultanahmet Square. Istanbul Governor Ali Yerlikaya said ahead of the Friday prayers, "Muslims are excited, everyone wants to be at the opening." Orthodox Church leaders in Greece and elsewhere, however, said that they would observe “a day of mourning” for the inaugural ceremony. On July 10, a High Court ruling in Turkey permitted Istanbul’s historic Hagia Sophia to be turned into a mosque. Shortly after the court made its decision, President Erdoğan announced that the former cathedral would be opened for worship as the “Ayasofya Mosque”. The court ruling overturned a 1934 decision to end use of Hagia Sophia as a mosque and instead turn it into a museum. Built 1,500 years ago as the premier cathedral in the Eastern Roman Empire, it was first converted into a mosque in 1453 when the Ottomans conquered Constantinople. The Turkish government has announced that Christian iconography uncovered during its time as a museum will now once again be covered up. Many church leaders have spoken critically of the decision. Pope Francis said he was "very pained" by the decision and Ecumenical Patriarch Bartholomew, Archbishop of Constantinople, told the Washington Post he was “saddened and shaken.” Despite an international backlash, with prominent criticism from UNESCO, the European Union and the United States, President Erdoğan insisted that Turkey was merely exercising its “sovereign rights”. “This is Hagia Sophia breaking away from its captivity chains,"  Erdoğan said last week. "It was the greatest dream of our youth.”