The Church of Hagia Sophia in Constantinople is a purpose-built structure, and its purpose is the worship of the Christian God. 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.

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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 Turkish government's response to the criticism has been positively schizophrenic. Erdogan and his deputies tend to rhetorically oscillate between the language of national sovereignty and the language of Islamic expansionism. On the one hand, a deputy chairman in the governing party told a local publication that "estranging a structure, the property of which belongs to Turkey, was going against our sovereignty." On the other, Erdogan himself said in a public address that "the resurrection of Hagia Sophia [as a mosque] follows the express will of Muslims throughout the world" and will serve as a first step towards "the liberation of Al Aqsa" in Jerusalem. Even before his speech, crowds had gathered outside Hagia Sophia chanting "Onward to Jerusalem!" In what will come as a shock to absolutely no one, it seems that many Turks do not believe that national sovereignty obtains for Israel. Hamas was quick to endorse Erdogan's decision.

The religious vision of pan-Islamic civilization that appears to drive Erdogan's attempts to dismantle the secular constitution of Turkey, a document of which many Turks are still very proud, does not stand up to any kind of scrutiny. In historical terms, there is vanishingly little evidence of Islamic civilization to begin with. Most of the great achievements attributed to Islamic cultures have been those of conquered peoples, or dhimmis, to use the theological term, whose work has been co-opted by their conquerors. Hagia Sophia is a case in point. 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 [Assyrian] Christian medicine; even the leading Muslim and Arab physicians were trained at the enormous Nestorian medical center at Nisibus in Syria." It was the Nestorian Christian Johannitius who collected and supervised the translation of Hippocrates, Galen, Plato, and Aristotle into Arabic. Furthermore, a Muslim writer of the eleventh century, Nasir-i Khrusau, reported that "the scribes here in Syria, as is the case of Egypt, are all Christians. . . . It is [also] most usual for the physicians . . . to be Christians."

There are countless examples of this dynamic, and they have been chronicled exhaustively by Stark and historians such as Donald R. Hill. The idea of Islamic civilization, which regularly threatens the security of Israel, the West, and anyone unfortunate enough to live under the rule of men such as Erdogan, resembles nothing so much as a great act of intellectual-property theft.

Worse yet, this great fiction has real-world consequences beyond the religious annexation of Hagia Sophia. Erdogan has offered very generous military aid to the Libyan government in Tripoli as it fights a war against the insurgent Haftar in Benghazi. He's described Turkish military casualties in the conflict as "martyrs" in the tradition of the Ottoman soldiers who fought in Libya from the 16th through 20th centuries. And following his announcement about the reconversion of Hagia Sophia, the Turkish Media outlet Haber 7 tweeted, "Hagia Sophia is done! Next is Athens." Sentiments such as this suggest that the spirit of conquest among devout Muslim Turks has increased rather than decreased since the country's secular founding in the 1930s. In this respect, Western governments have made the same mistake with Turkey as they have with China, assuming axiomatically that exposure to liberal-democratic capitalism increases the desire for it over time. The truth is that Turkey and many other conservative Islamic countries are taking a different path through the 21st century than the United States and its allies. The holy texts of Islam suggest that this path will not be one that seeks to avoid conquest. According to the Hadith of Sahih Bukhari, the Prophet Muhammad himself claimed to have "been made victorious with terror" (4:52:220). The actions not only of Turkey in Libya but of Saudi Arabia and Iran in Yemen testify to the lasting impact of this sentiment upon the author's religious progeny.

The United States cannot continue to deal with Islamist countries as if they were nation-states like any others. Turkey and its allies have learned to use Western concepts such as "national sovereignty" in pursuit of their own theocratic, imperialist ends. If they are not challenged robustly when they employ this tactic to win huge symbolic victories, as they have with Hagia Sophia, they will only feel more emboldened to reach for it again when lives are on the line instead of mosaics. Turkey's status as a member of NATO and its potential accession to full membership in the European Union should be conditional upon the rejection of political Islam and the total cessation of all rhetorical or military hostility toward Greece, Cyprus, Israel, and the West in general. Entry into the Western community of nations must be contingent on adherence to a standard of civilized government, and until it is, American leaders should highlight the problem as often, as forcefully, and as publicly as they can. History teaches us that the moment Islam shifts from spiritual discipline to governing philosophy, free "infidels" have cause for concern. After 85 years of secular Turkish government, it looks like President Erdogan is effecting that shift once again. If Turkey is to receive any more economic, military, or diplomatic favors from the Western world, Hagia Sophia should either be returned to its status as a museum or remanded into the care of the Greek Orthodox Church, for whose liturgy and worship it was purpose-built so many centuries ago.