The Muslims soon destroyed the bells, altar, iconostasis, and other relics, and the mosaics depicting Jesus, his mother Mary, Christian saints, and angels were eventually destroyed or plastered over. Islamic features – such as the mihrab (a niche in the wall indicating the direction toward Mecca, for prayer, the minbar (pulpit), and four minarets – were added. It remained a mosque until 1931 when it was closed to the public for four years.

It was re-opened in 1935 as a museum by the Republic of Turkey, the secularist state created by Kemal Ataturk. It officially remains a museum until today, but it is steadily assuming more and more features of a mosque. And any day now, in the re-islamizing spirit of President Recep Tayyip Erdogan, many believe the museum will almost certainly again become a mosque. But the Turkish tourism industry may have its own ideas.

In May 2019, Erdoğan said: “A short time ago [is 85 years such a short time?] they [the Kemalists] converted the Hagia Sophia from a mosque to a museum. Inshallah, after the election, we will convert it – namely, from a museum back into a mosque.” Even before Erdogan’s ascendance, beginning in 1980 the Islamic call to prayer was recited in the building. But those were performed by individual Muslims, without any official sanction. Ever since Erdogan has been in power, there have been discussions in the government about converting the building back into a mosque.

On May 30, 2016, the 563rd anniversary of the conquest of Constantinople, supporters of the Saadet (“Felicity”) party, an Islamist party, wearing t-shirts that said “Shoes cannot be worn in a mosque,” took their shoes off at the entrance of the Hagia Sophia and walked around inside without their shoes on. In their reasoning, by taking their shoes off as they would have had to do in a mosque, this made the building less like a museum, and more like a mosque.

During Ramadan in June 2016, the Ministry of Religious Affairs televised a special program on its Diyanet TV channel in which verses from the Quran and calls of tekbir (“Say: Allah is greater”) were recited from the minarets of the Hagia Sophia. Everyone understood this as one more step in the museum-to-mosque transformation. In October 2016, Turkey’s Ministry of Religious Affairs appointed an imam to the Hagia Sophia. This was the first time since 1931 that the building had an imam. Prayers were now performed regularly. Noon and afternoon prayers had been heard in the building since 1991, but since late 2016 all five of the canonical daily prayers have been performed.

Now that both the Friday Prayers, presided over by the appointed imam, and the five daily prayers (one of them being the Friday Prayers), were being heard, it was natural for Erdogan in 2018 to promise that he would turn the Hagia Sophia from a museum into a mosque. He reiterated that promise in March of 2019: “Hagia Sophia will no longer be memorialised as a museum. Hagia Sophia will be commemorated as a mosque. This is our people’s expectation, and that of the Muslim world. Our people have longed to see Hagia Sophia as a mosque for years.”

And a recent decision by Turkey’s Council of State provides him with more support for turning Hagia Sophia back into a mosque. The decision was not about the Hagia Sophia itself, but about the second great Christian church-turned-museum in Istanbul, the Church of St. Savior in Chora. This medieval building, a thousand years old, was converted into the Kariye Mosque in the early 16th century by an Ottoman vizier, and was then designated a museum by the Turkish government in 1945. Its 14th-century frescos and mosaics are regarded as among the world’s finest examples of Byzantine art.

Most of those frescoes and mosaics were plastered over by Muslims while the building was a mosque, which allowed them to avoid the kind of destruction that was visited upon the interior of the Hagia Sophia. Turkey’s Council of State, the country’s top administrative court, in November 2019 ruled that the cabinet decision in 1945 that made Kariye a museum was unlawful because a mosque “cannot be used except for its essential function.” In other words, once a mosque, always a mosque. Ataturk and his secularist followers be damned. The Council of State ordered that the museum of the Church of St. Savior in Chora be turned back into a mosque.

The ruling has obvious repercussions for other monuments from Turkey’s Christian past, especially the Hagia Sophia. Islamists have long prayed for both the Chora Church and the Hagia Sophia to reopen as mosques, arguing that their neutral status is an affront to the Ottoman caliph’s decrees forbidding other uses. And now it has so been ordered for the Chora Church and, by obvious implication, the Hagia Sophia. Two of the most important Christian sites will again be full-fledged mosques.

Will the masterpieces of Byzantine art in the Chora Church again be plastered over so as not to offend Muslim worshippers? It would be a great loss for world art. And what would happen to what remains of the Christian art on the walls of Hagia Sophia – much of it was destroyed, vandalized by Muslims when the building was used as a mosque, though some still exists, albeit damaged –if that building again becomes a mosque? The two sites are inscribed on Unesco’s World Heritage list, which recognises the “architectural masterpieces” of Istanbul.

The agency has said in the past that changes in the status of the city’s historic monuments would undermine their heritage value. If Chora Church and Hagia Sophia again become mosques – and their Christian art covered over and no longer visible to visitors — will they lose their prized places on that World Heritage list? Other Byzantine sites converted into mosques have covered frescos to comply with Islamic tenets prohibiting the use of images. But for much of the Ottoman period, Muslims worshipped at Chora and other former churches in view of the art, says Edhem Eldem, a professor of history at Bogazici University.

Turning Chora into a museum served as a compromise between Muslims and Christians, he says, adding that the current uneasiness around Turkey’s Byzantine heritage is part of the “politics of populism that appeal to basic feelings of ethnic, national and religious identity.”The Hagia Sophia is the most important attraction for visitors – at least two million a year – in all of Turkey. Will Christians continue to visit Istanbul when its two most famous Christian sites have become mosques, or will seeing them thus transformed, and with their Christian art likely covered over, be too painful for Christian visitors?

Many businesses and jobs in Istanbul depend on tourism, and especially on Christian tourists who come to see the Hagia Sophia and the Chora Church. Might the economic interests of those many Turks whose livelihood depends on tourism in the end prove too powerful politically for Erdogan to overcome? Erdogan’s party has already lost Turkey’s three major cities – Istanbul, Ankara, and Izmir –to the opposition. He could be put on the defensive by his political opposition, which could argue that in turning the Chora Church museum back into a mosque, he had done enough of what his Muslim followers wanted, but that were he to turn Hagia Sophia into a mosque, the economic damage to the country, in its loss of tourism dollars – currently Turkey derives $40 billion from its tourism industry – would be catastrophic.

Turkey’s economic situation is already parlous; it doesn’t need any self-inflicted wounds. Besides, that secularist opposition could note, in Hagia Sophia, despite its status as a museum, the five daily prayers are said and the building has been assigned its own imam. Erdogan could argue that the museum has thereby effectively taken on the most important aspects of a mosque. “It is again a mosque in the hearts of Believers.” All Turks would understand that he had been made to realize the possibly grievous damage to tourism, should Hagia Sophia be officially declared a mosque, and the damage as well to his own political fortunes, for the tourism business in Turkey constitutes a powerful economic lobby.