Context
By the mid-15th century, the Byzantine Empire had been reduced to little more than the city of Constantinople and a few surrounding territories. Once the heart of a vast empire stretching across three continents, Byzantium had been steadily eroded by centuries of warfare, internal strife, and the rise of powerful neighbors. The Fourth Crusade’s sack of Constantinople in 1204 had dealt a devastating blow from which the empire never fully recovered, while the gradual expansion of Ottoman power in Anatolia and the Balkans had systematically consumed Byzantine territories.
The Ottoman Empire under Mehmed II represented the most formidable threat Constantinople had ever faced. The young sultan, who had ascended to the throne in 1451 at age 19, was determined to complete what his predecessors had attempted: the conquest of the last remnant of the Roman Empire. The Ottomans possessed significant advantages including a large, disciplined army, a powerful navy, and most crucially, advanced artillery technology that could breach the massive walls that had protected Constantinople for over a millennium.
Emperor Constantine XI Palaiologos ruled over a city with perhaps 50,000 inhabitants, a fraction of its former population. The Byzantine treasury was empty, the military numbered only a few thousand soldiers, and hopes for substantial Western aid remained largely unfulfilled despite desperate diplomatic efforts. The emperor understood that the upcoming siege would likely determine not just the fate of his city, but the end of an empire that traced its lineage back to Augustus Caesar.
The Siege
Mehmed II began his preparations in earnest during 1452, constructing the fortress of Rumelihisarı on the European shore of the Bosphorus to control access to the Black Sea and commissioning massive cannons from Hungarian engineer Orban. The siege officially began on April 6, 1453, when Ottoman forces estimated at 80,000-100,000 men surrounded the city’s landward and seaward approaches. The Byzantines could muster only about 7,000 defenders, including approximately 2,000 foreign volunteers, primarily Genoese under the command of Giovanni Giustiniani.
The siege’s most remarkable feature was the Ottoman employment of massive cannons, including Orban’s great gun that could fire stone balls weighing over 600 pounds. These weapons systematically pounded the Theodosian Walls, which had protected the city since the 5th century. When the Ottoman fleet was initially blocked by a chain across the Golden Horn, Mehmed ordered ships to be transported overland on wooden rollers, launching them behind the Byzantine naval defenses in a stunning logistical achievement that demoralized the defenders.
After nearly two months of bombardment and several failed assaults, Mehmed ordered the final attack for May 29, 1453. The assault began before dawn with waves of irregular troops followed by regular infantry and elite Janissaries. Constantine XI, reportedly fighting in the thick of battle, was killed during the final assault, his body later identified among the fallen. By mid-morning, Ottoman forces had breached the walls and poured into the city, effectively ending over 1,100 years of Byzantine rule.
Consequences
The immediate aftermath saw Constantinople transformed from a Christian imperial capital into the center of an expanding Islamic empire. Mehmed II, now styling himself “Caesar of Rome,” converted the Hagia Sophia into a mosque and began extensive rebuilding efforts to restore the city’s former glory. The Ottoman capital was moved from Adrianople to Constantinople, which gradually became known as Istanbul, though this name wasn’t officially adopted until the 20th century.
The fall had profound implications for European geopolitics and culture. Many Greek scholars fled westward, bringing with them classical manuscripts and knowledge that contributed to Renaissance humanism. The Ottoman control of traditional trade routes to Asia encouraged European exploration of alternative paths, indirectly spurring the Age of Discovery. The conquest also shifted the balance of power in southeastern Europe, with the Ottoman Empire now positioned to expand further into the Balkans and challenge Habsburg Austria.
The event became a powerful symbol marking the transition from medieval to early modern periods. For Orthodox Christians, particularly Russians, the fall represented a catastrophic loss, contributing to Moscow’s later claims as the “Third Rome.” In the Islamic world, the conquest was celebrated as a great victory fulfilling prophetic traditions about the conquest of Constantinople. The successful use of gunpowder artillery also demonstrated the changing nature of warfare, showing that even the strongest medieval fortifications could be overcome by new military technologies.
Key Developments
- 1204: Fourth Crusade sacks Constantinople, permanently weakening Byzantine Empire
- 1354: Ottomans establish first permanent foothold in Europe at Gallipoli
- 1394-1402: First Ottoman siege of Constantinople fails due to Mongol invasion of Anatolia
- 1422: Second Ottoman siege under Murad II unsuccessful
- 1451: Mehmed II becomes Ottoman Sultan, begins planning Constantinople’s conquest
- 1452: Construction of Rumelihisarı fortress controls Bosphorus, Hungarian engineer Orban joins Ottomans
- February 1453: Mehmed’s great cannon successfully tested outside Constantinople
- April 6, 1453: Ottoman siege begins with bombardment of Theodosian Walls
- April 20, 1453: Three Genoese ships break through Ottoman naval blockade bringing supplies
- April 22, 1453: Ottoman fleet transported overland into Golden Horn behind Byzantine defenses
- May 12, 1453: Major Ottoman assault repelled by defenders
- May 18, 1453: Ottoman attempt to tunnel under walls discovered and defeated
- May 26, 1453: Mehmed offers final terms for surrender, rejected by Constantine XI
- May 29, 1453: Final assault begins at dawn, city falls by afternoon, Constantine XI killed
- June 1, 1453: Mehmed II enters Hagia Sophia, orders its conversion to mosque