[custom_adv] Several thousand Muslims gathered on Friday to take part in the first prayer at Hagia Sophia since the Istanbul landmark was reconverted to a mosque, with Turkish President Recep Tayyip Erdogan also expected to take part. [custom_adv] Despite the coronavirus pandemic, tight crowds formed on Friday morning around the former cathedral for the prayer scheduled for around 1000 GMT, AFP correspondents said. Several people had spent the night in the area. [custom_adv] The UNESCO World Heritage site in historic Istanbul was first built as a cathedral in the Christian Byzantine Empire but was converted into a mosque after the Ottoman conquest of Constantinople in 1453. [custom_adv] The Council of State, the highest administrative court, on July 10 unanimously cancelled a 1934 decision by modern Turkey's founder Mustafa Kemal Ataturk to turn it into a museum, saying it was registered as a mosque in its property deeds. [custom_adv] Erdogan then ordered the building to reopen for Muslim worship, deeply angering the Christian community and further straining relations with NATO ally Greece. [custom_adv] Erdogan's decision has also undone part of the secular legacy of Ataturk, who wanted Hagia Sophia as a museum so as to "offer it to humanity". [custom_adv] The timing of the first prayer is significant. Friday is the 97th anniversary of the Treaty of Lausanne, which set modern Turkey's borders after years of conflict with Greece and Western powers.