This particular function is not incidental to the way the church was designed and built by its two visionary architects at the high meridian of the Byzantine Empire. Anthemius of Tralles and Isidore of Miletus were what their contemporaries called mechanopoioi, a term that is best translated, according to Richard Krautheimer, as “architect–scientists.” Their elite proficiency in mathematics and physics suited them to the task they’d been given by the emperor: building an originally Christian place of worship. In the sixth century, Christians were still drawing on the aesthetics of pagan antiquity, and the basilicas and colonnades of classical Rome had been accepted as the supreme expression of architectural grandeur. Hagia Sophia changed all that.

When Emperor Justinian entered the church for the first time after its completion, he is said to have boasted, “Solomon, I have vanquished thee!” He, or rather his two architects, certainly had. With an interior space of almost 43,000 square feet, it was at the time the single-greatest building ever constructed. Its crowning jewel was its gravity-defying central dome, which in a single stroke supplanted the basilica as the defining feature of church architecture in Eastern Christendom. The dome serves as a mirror to heaven, believed in late antiquity to be the most distant in a series of concentric spheres, and its 40 windows allow light from above to shine upon the glittering religious mosaics inside the church. But its most important religious function is musical.

The interior of Hagia Sophia was designed for the antiphonal singing of the Christian liturgy, with two choir sections alternating chants across from one another. The dome captures and enhances the sound of this exchange. Musical notes usually reverberate for two to three seconds in a modern concert hall. In Hagia Sophia, they resound for up to twelve seconds, enveloping worshippers in the sounds of the liturgy — or at least they did, until the Ottoman conquest of Constantinople in 1453. For 482 years after that, Hagia Sophia was used as a mosque. In the 1930s, when Turkey was born from the ashes of the Ottoman Empire as a secular state, the mosque was repurposed once more as a museum for Christians, Muslims, and any other admirers to visit.

But now, that state is being systematically remade by President Recep Tayyip Erdogan, who has come to dominate Turkish politics with his own malevolent brand of neo-Ottoman Islamic nationalism. Erdogan has long sought to reconvert Hagia Sophia into a mosque, and this week he was finally granted his wish by the Turkish Council of State. The Council’s legal reasoning was about as risible as one could possibly imagine: It ruled that the initial conversion of the church into a museum in 1934 was unlawful, because Hagia Sophia was the personal property of Mehmet the Conqueror, the sultan who captured the city in 1453.

The Council then transferred control of the museum to a foundation named after the sultan, which is in favor of its repurposing as a mosque. There are many problems with this ruling, but chief among them is the fact that under 15th-century Ottoman law, as Professor Metin Günday has observed, the entire country was the personal property of the sultan. The legal precedent set in the case of Hagia Sophia seems to suggest that through the shell foundation named after Mehmet II, any living heir of the sultan can lay personal proprietary claim to the entire nation of Turkey and all of the property therein!

What’s more, the Church of Hagia Sophia has now been reduced to the same legal status it held at the sack of Constantinople, with Muslims worshipping there on the legal basis of Mehmet’s bloody conquest of the Christian population. It is true that the conquest ethic was, until very recently, universal in human relations, and it does no one any good to condemn the actions of medieval men in this regard or to adjudicate property disputes accordingly. To call Mehmet the Conqueror a violent and oppressive warlord is merely to observe that he was a political leader in the middle of the 15th century. But for a court of law to resurrect the logic of medieval conquest in the 21st century is truly appalling.

To repeat: Christians’ access to one of their greatest holy sites will now be greatly curtailed on the grounds that they were conquered by a Muslim sultan and forced into what can only be described as sacred-asset forfeiture at the point of a sword more than 500 years ago. The global response to Erdogan’s move has ranged from indifference to outrage. The Turks have close ties with Moscow, and the Russian deputy foreign minister said last Monday that changing the status of the church to a mosque was the internal business of the Turkish government. (Given the way in which the Kremlin has sought to blur the lines between Orthodox Christianity and Russian Nationalism, its acquiescence to the desecration of an iconic, non-Russian Orthodox church is perhaps unsurprising.)

By contrast, the Greek culture minister called Erdogan’s move an “open provocation to the civilized world” in a statement on Friday, and the Greek government is pushing for the European Union to impose diplomatic sanctions on Turkey. The leader of the Italian Northern League, Matteo Salvini, has also criticized the decision, citing it as evidence that “the pre-eminence of Islam is incompatible with the values of democracy, freedom and tolerance of the West.”The dome that was so ingeniously designed by Anthemius and Isidore has been used as the model for mosque architecture ever since. Indeed, when Caliph Abd el-Malik commissioned the Dome of the Rock, now considered one of the great masterpieces of Islamic art, to be built in Jerusalem, he employed Byzantine architects and craftsmen, which is probably why the structure looks so much like the same city’s Church of the Holy Sepulchre.

“To the extent that Arab elites acquired a sophisticated culture, they learned it from their subject peoples,” the sociologist Rodney Stark has noted. The much-vaunted “Arabic” numeral system is in fact Hindu in origin, based on the concept of zero, which had theretofore eluded the Muslim overlords of Hindu populations. The earliest scientific text that appeared in Arabic, the holy language of Islam, was translated by a Jewish physician from the work of a Syrian Christian priest in Alexandria, which would have surprised no Arabian Muslim of that time. As Stark notes, “‘Muslim’ or ‘Arab’ medicine was in fact Nestorian Christian medicine; even the leading Muslim and Arab physicians were trained at the enormous Nestorian medical center at Nisibus in Syria.”