For the second time in its history, Hagia Sophia has been turned into a mosque. The first time was after the Ottoman conquest of Constantinople in 1453. Atatürk turned it into a secular museum in 1934. Last Friday, a court ruled that conversion to have been illegal. The first prayers will be held on 24 July, the anniversary of the 1923 Treaty of Lausanne. The move is widely seen as the latest step in the Islamisation of Turkish society under Recep Tayyip Erdoğan and the AKP.