Twenty-twenty has been an interesting year for national monuments. In America, statues have been toppled on public squares everywhere, even as President Trump declares a heroic past beneath the stony visages of Mount Rushmore. In Russia, victory over Nazi Germany has been commemorated by the construction of a cathedral—one of the largest in the world—whose consecration brought President Putin alongside Patriarch Kirill. And in Turkey—once the heartland of Eastern Christendom, the majestic Hagia Sophia has now been designated by President Erdogan a national mosque.

The story of this famous monument is a tale of political commemorations, and one of the longest in history. It starts with Byzantium, the name historians give to the Eastern Roman Empire after the conversion of Constantine to Christianity in the fourth century. The first Christian emperor moved his capital to Constantinople in part because Rome’s landscapes were overwhelmed by monuments to paganism. Constantinople, he insisted, would be a city with only Christian monuments.

Situated on a bluff overlooking Europe’s gateway to Asia, Hagia Sophia was in fact a symbol of the world’s ongoing conversion to Christianity. In the sixth century Emperor Justinian completely rebuilt it with a huge central dome in order to symbolize the sanctification of the cosmos. Upon completion he declared the cathedral surpassed in glory even the Temple of Solomon.

Naturally, Byzantium’s enemies could not leave Hagia Sophia and the Orthodox Christian civilization it represented alone. Wave after wave of Persian, Arab, and Slavic armies did their best to acquire it over the centuries. It was only Roman Catholic crusaders who finally succeeded in 1204, when the cathedral was stripped of its wealth and made the seat of a short-lived Latin Patriarchate. After reconquering Constantinople, the Orthodox again ruled there until 1453 when the Turks finally put an end to the Byzantine state. On the very day the city fell to their armies, in fact, Sultan Mehmet II rode directly from the breached city walls to the cathedral and ordered a Muslim cleric declare the shahadah from the same pulpit used by Christian bishops stretching back to John Chrysostom. The cross was toppled from the central dome like a statue of General Lee in the hands of Antifa demonstrators, and an image of the crescent hoisted into its place.

Only in 1935 was the building reduced to the status of a museum to advance the ideals Ataturk’s secular nationalism. Today, those ideals are receding as the tide of resurgent Islam slowly inundates Turkey. And so Hagia Sophia again has been made to serve as a monument to something—in this case a state—that one day must pass away.

But the history of Hagia Sophia is more than a tale of political fortunes. It is also a tell-tale of two “cities,” of two distinct spiritual dispositions. One is of the world, and one is not.

The most famous of ancient churches was built so that the faithful within it, when assembled for worship, stood facing eastward. In other words, it was defined by “orientation.” The Latin word oriens literally means “east,” and Christians from the earliest times insisted that their temples be oriented. They did so for one very important reason: the east symbolized the kingdom of heaven, or paradise, which according to the gospel is not of this world.

Genesis had located the Garden of Eden in the east (Gen. 2:8), and from an early point Christians used such directional symbolism as a guide to sacramental worship. Communion with Christ was nothing short of paradise, after all, and being oriented by worship meant being joined to the messianic “Sun of Righteousness” who, like the morning star, promised to return “like lightening  comes from the east” (Mal. 4:2; Matt. 24:27). By the fourth century, Basil the Great spoke of liturgical orientation as an established fact and claimed it was a tradition handed down from the apostles.

Hagia Sophia was thus built as a monument not to this world, but to the eternal kingdom of heaven. And in doing so it established a precedent for the innumerable other churches of Christendom—from Notre Dame in Paris to Saint Paul in London to National Cathedral in Washington, D.C.—that for more than a millennium have done likewise. The principle of architectural orientation proclaims to the faithful that, in the words of the apostle, “here we have no continuing city” (Heb. 13:14).

Not so, Islam. While it also holds to a belief in an eternity beyond this world, it directs worship toward a place on earth, Mecca. It even requires every mosque be built with a niche in the wall called a mihrab that indicates the direction of Muhammad’s city. Thus Muslims, when in prayer, face eastward if they are in the western hemisphere but westward if living in a land such as Indonesia. In the case of Turkey, they face southward.

So, soon after the Turkish conquest of Constantinople a mihrab was installed within the apse of Hagia Sophia just to the south of the former altar’s center point. It is still there today, and soon will become much more prominent as the building reverts to a mosque. In fact, for the time being a Byzantine icon of the Virgin Mary holding Christ, restored during the building’s museum period, is even visible above it.

Throughout history, Hagia Sophia has been the envy of empires and the spoil of their conquests. As an architectural wonder, it not only enhanced the Byzantine state but stood as monument to the Christian culture that surpassed it. This is why, no doubt, the heirs of Christendom—from church leaders to cultural preservationists—have expressed alarm at the recent news it will again serve as a mosque.

But Christians really have nothing to lament. After all, even when it was the greatest cathedral on earth, it never did more than proclaim the evangelical conviction that the glory of this age is nothing when placed in the presence of the kingdom of heaven.

If the history of Hagia Sophia is the tale of two cities—one earthly and the other heavenly—then the cathedral’s greatest service to Christians today is to remind them that here on earth they have no continuing city. Like a heavenly tell-tale, it points ever-eastward, beyond Constantinople and Mecca, to the city of God.