The basic facts
Constantinople fell to the Ottoman army of Sultan Mehmed II on 29 May 1453, after a siege that began in early April. The date is firmly established. The “fall” was less a sudden surprise than the end of a long decline: by the early fifteenth century the Byzantine Empire consisted of little more than the city itself, a few islands and coastal holdings, and parts of the Peloponnese, and its emperors depended on tribute arrangements and foreign help.
The conquest is sometimes described as the moment the Middle Ages ended. That is a convenient shorthand rather than a fact. Historians use several markers for the shift to the early modern period, and the date mostly matters because it ended a Roman state that traced itself back more than a thousand years.
Preparing for the siege
Mehmed II was a young sultan, still in his early twenties, and he had reasons to want the city. It sat across the main crossing between his European and Anatolian lands, and Constantinople’s continued independence was a standing political problem.
His preparations included building a fortress, Rumeli Hisari, on the European shore of the Bosphorus in 1452, which helped control shipping. He also assembled a large army and a fleet, and hired or relied on engineers who could cast and use very large cannon. Sources disagree on exact troop numbers. Defenders and attackers both left figures, but medieval chroniclers often exaggerated, so most historians prefer to say only that the Ottoman force greatly outnumbered the defenders, who probably numbered a few thousand fighting men in total.
The last emperor, Constantine XI, had sought help from the West for years. A proposed union of the Greek and Latin churches was one price of that help, and it caused bitter divisions inside the city. A modest force of Italian volunteers and Venetian and Genoese residents arrived, and Genoese commander Giovanni Giustiniani Longo is often named as a key figure in the defense. But no large relief army came.
The siege
Constantinople’s greatest advantage was its land walls, the Theodosian Walls, a multi-layered system built in the fifth century that had withstood many attacks. The defenders also stretched a chain across the Golden Horn to keep enemy ships out of the inlet. Many earlier attempts, including each siege of Constantinople by Arab and other forces, had failed against them.
During the siege the Ottomans bombarded the walls with large guns, which damaged sections but needed long pauses between shots and constant repair work by the defenders. A well-known episode, which sources report with some variation, is the movement of Ottoman ships overland on greased logs into the Golden Horn, bypassing the chain and forcing the defenders to guard a longer line. The details of how this was done are debated.
The final assault came in the early hours of 29 May. After several waves, Ottoman troops broke through, possibly aided by the wounding or withdrawal of Giustiniani and by confusion at a small gate. Constantine XI is believed to have died fighting, but the circumstances of his death are not known with certainty, and many legends grew up around it.
Sack and settlement
After the city fell, it was plundered for a period, following military custom of the time. Many inhabitants were killed, and many others were enslaved or taken captive. Sources describe the scale differently, so exact casualty figures should be treated cautiously. Mehmed soon ordered the looting stopped, since he wanted a functioning capital.
Over the following years, the sultan encouraged people to settle in the city, including by moving families from other parts of his realm, in some cases forcibly. Greek Orthodox leadership was kept in place under a new patriarch, Gennadios, who was recognized by the sultan, and Jewish and Armenian communities also grew in the city over time. The Genoese colony of Galata across the Golden Horn was allowed to continue under terms.
Hagia Sophia was converted into a mosque, and later buildings, including a palace and new religious complexes, reshaped the skyline. The city gradually became the Ottoman capital, later known as Istanbul, though that name came into official use only over time.
Effects on the region
The capture removed the last substantial obstacle to Ottoman control of the Straits. Over the following decade Mehmed took most of the remaining Byzantine territory, including the Morea (the Peloponnese), and the Empire of Trebizond on the Black Sea coast fell in 1461. Serbia, Bosnia and Albania faced growing pressure, and Ottoman power moved north toward the Kingdom of Hungary.
For Italian trading cities, the change meant renegotiating terms. The Venetian republic and Genoese merchants were both affected, as trade and colonial positions in the Aegean and Black Sea came under Ottoman influence. Venice made peace and kept trading privileges, while Genoese holdings in the Black Sea were lost over the next decades.
Western reaction and legacy
News of the fall alarmed Western rulers, and the pope called for a crusade. Little came of it in practice, because rulers were absorbed in their own conflicts. The Hundred Years War, for instance, was only just reaching its end in France. Some Byzantine scholars migrated west, and a long-standing claim says they sparked the Renaissance. Most historians now regard that as an oversimplification: Greek learning was already reaching Italy before 1453, and the arrival of more scholars was one influence among many.
The broader legacy is mixed. For the Ottomans, 1453 confirmed the dynasty as an imperial power with a famous capital. For Greeks and Orthodox Christians it began centuries of life under Muslim rulers, with a flexible but unequal legal framework. For Europeans, it became an emblem of loss, shaping fears and propaganda about the Ottomans for generations. How people remember the conquest still varies a great deal depending on whether they inherit the Greek, Turkish, Italian or wider European tradition.