For a thousand years, the city of Constantinople had stood as the bridge between East and West, a bastion of Christian empire facing the Islamic world. By the mid-fifteenth century, however, the walls that had repelled armies for centuries were surrounded once again.

The Ottoman Empire, ruled by the ambitious Sultan Mehmed II, had conquered almost all of the old Byzantine lands. Only the capital remained, its emperor ruling a city of fewer than a hundred thousand souls.

In April 1453, Mehmed’s great army appeared before the city. Behind the soldiers marched cannon teams hauling bronze bombards so huge that they needed sixty oxen to move them. Inside the walls, Emperor Constantine XI gathered every able man he could find, praying that help from Christian Europe would come. None did.

The siege lasted fifty-three days. Every dawn brought another storm of cannon fire. When the final assault came on 29 May, it began before sunrise and ended by noon. The walls were breached, the defenders cut down, and the banner of the Prophet raised above Hagia Sophia, the greatest church of Christendom. By nightfall, Constantinople, once the eastern capital of the Roman Empire, had become the new jewel of Islam.

The shock of a new power

For Christian Europe, the event was an earthquake. “A thunderclap that awoke the nations,” wrote Aeneas Silvius Piccolomini, later Pope Pius II. The loss of Constantinople was more than a military defeat; it was a symbol of how far the balance of power had tilted.

The Ottoman Empire now ruled the Balkans and the eastern Mediterranean, while Western Christendom remained fragmented. France and England were exhausted after the Hundred Years’ War, Italy was divided among rival city-states, and the German princes quarrelled within the Holy Roman Empire. The papacy, weakened by schism and corruption, could no longer unite them.

Yet out of this division a new awareness began to form. Confronted by a dynamic and expanding Islamic power, Europeans began to imagine themselves not merely as rival kingdoms but as part of a shared civilisation. They began to use a new word to describe it: Europe.

The useful enemy

The historian Sir Noel Malcolm, senior fellow at All Souls College, University of Oxford, explores this transformation in his book Useful Enemies: Islam and the Ottoman Empire in Western Political Thought, 1450–1750. He argues that the confrontation between Islam and Christianity was not only a clash of armies but a contest of ideas that helped to define the modern West.

The Ottomans, he writes, were: “useful enemies,” powerful enough to terrify, disciplined enough to inspire admiration, and ever-present enough to force Europe to imagine itself.

Before 1453, the concept Europe was mostly abstract. After the fall of Constantinople, it gained moral and political meaning. Pius II appealed to the princes of Christendom to unite as: “sons of Europe” against the Turks. The term Christendom still carried religious weight, but Europe introduced something new: a vision of civilisation itself, ordered, learned, and free, standing against an empire of faith and force.

Observers saw in the Ottoman state both a rival and a reflection. Venetian diplomats praised its efficiency, its soldiers’ discipline, and its system of law.

Thinkers such as Niccolò Machiavelli in Florence and Jean Bodin in France studied it to understand how power could be centralised and maintained. By condemning the sultan’s: “despotism,” they refined their own ideas of liberty and limited government. Europe’s political thought matured in the mirror of Islam.

From fear to identity

Over the next two centuries, the Ottoman challenge forced Europe’s divided kingdoms to cooperate and compete in new ways. Initially, crusading zeal gave way to strategy and diplomacy. The rivalry with Islam encouraged technological innovation, stronger states, and a balance between faith and reason. Even during the Protestant Reformation, when Christians fought each other in the name of doctrine, the Ottoman presence reminded them of a larger world and of what could be lost if they remained divided.

By the seventeenth century, scholars such as Hugo Grotius in the Netherlands and Samuel Pufendorf in Germany began to speak of a “society of European states,” bound by common laws even when faiths differed. Centuries of trade, warfare, and negotiation with the Ottoman Empire had taught Europeans that civilisation required rules of coexistence as well as courage.

The siege that united Europe

That long lesson reached its climax in 1683, when the Ottoman Empire made its final and most daring thrust into Central Europe. A vast army under Grand Vizier Kara Mustafa Pasha marched on Vienna, the gateway to the continent.

The city’s fall would have opened the Danube plain to Ottoman conquest and perhaps extinguished the idea of Europe altogether.

After months of siege, Vienna was starving, its walls shattered. Then, on 12 September, salvation arrived from the north. King John III Sobieski of Poland led a coalition of forces that had gathered under the banner of mutual survival. They called themselves Europe’s army.

From the heights of the Kahlenberg, Sobieski’s cavalry assembled for the counterattack. At its heart stood the Polish Winged Hussars, elite horsemen clad in gleaming armour, their backs adorned with arcs of eagle feathers that rustled like wings in the wind. As church bells rang across the city, Sobieski raised his sword and gave the signal.

The charge that followed was one of the largest in history. Eighteen thousand cavalry thundered down the slopes toward the Ottoman lines. The earth shook beneath their hooves and sunlight flashed off steel and feathers. Within hours, the siege was broken and the Turkish army was in retreat.

To contemporaries, it felt like deliverance. Chroniclers wrote that the horsemen rode: “for Christendom, for Europe, and for all that was their way of life.” In the smoke and dust outside Vienna, the fragmented kingdoms of the West stood, for the first time, as one civilisation.

The Ottomans never conquered Europe, but they shaped it. The long rivalry between crescent and cross turned fear into identity and division into unity. Out of centuries of struggle, Europe discovered not only what it was defending, but who it was.

When the Winged Hussars rode at Vienna, they carried more than weapons; they carried the idea of Europe itself, a civilisation finally conscious of its name, its heritage, and its destiny.