On the morning of 29 May 1453, the Ottoman army of Sultan Mehmed II breached the land walls of Constantinople and took the city by storm, ending the Byzantine Empire — the surviving eastern half of the Roman state, governed in an unbroken line from the capital Constantine the Great had dedicated as New Rome on 11 May 330. The last emperor, Constantine XI Palaiologos, died in the fighting near the breach; his body was never identified with certainty. After a siege of roughly seven weeks, an empire that traced its authority to Augustus passed out of existence.
By 1453 that empire was already a husk. The polity Mehmed conquered was not the Mediterranean superstate of Justinian but a rump centered on a single decayed city, surrounded on every side by Ottoman territory and surviving largely on Ottoman sufferance. The decisive wound had been inflicted not by Muslims but by fellow Christians: the Fourth Crusade had sacked Constantinople in 1204, broken the empire into Latin and Greek fragments, and drained the strength it never recovered after the Greeks retook the city in 1261. What fell in 1453 had been dying for two and a half centuries.
The mechanism of the final conquest was a collision between an old technology and a new one. The Theodosian Walls, raised in the fifth century, had repelled assault for a thousand years and were the most formidable land fortification in the medieval world. Against them Mehmed brought the largest gunpowder siege train yet assembled, including a monstrous bronze bombard cast by the Hungarian engineer Orban. The walls that had defined the impregnability of Constantinople were, within weeks, reduced to a problem of arithmetic.
The fall reverberated far beyond the Bosporus. It severed the eastern land routes that had carried Asian goods to Europe through Constantinople, sharpening the search for sea passages that became the Age of Exploration; it scattered Greek scholars and manuscripts westward into a Renaissance hungry for them; and it gave the Ottomans an imperial capital they would rule for nearly five centuries. The conversion of the great church of Hagia Sophia into a mosque, ordered by Mehmed on the day of the conquest, fixed the moment in memory as the end of one age and the start of another.
In February 1258, the Mongol army of Hulagu Khan — a grandson of Genghis Khan — stormed Baghdad, the capital of the Abbasid Caliphate, and extinguished a dynasty that had claimed the leadership of the Sunni Muslim world for five centuries. The Mongols invested the city on or about 29 January, breached its walls within days, and accepted the surrender of the caliph al-Musta’sim on 10 February. The sack that followed killed an immense number of the city’s inhabitants, scattered or burned its great libraries, and left Baghdad a depopulated ruin. The caliph himself, the thirty-seventh and last of the Abbasid line, was executed on 20 February — rolled in a carpet and trampled to death by horses, by an account widely repeated, so that no royal blood would touch the ground.
The dynasty that ended had been founded in 750, when the Abbasids overthrew the Umayyads, and from its purpose-built capital at Baghdad, established in 762, it had presided over the most brilliant period of medieval Islamic civilization. By the thirteenth century, however, the caliphate’s real power had long drained away. For three hundred years the caliphs had reigned more than they ruled, their authority eclipsed first by Persian and then by Turkish military dynasties — the Buyids and the Seljuks — who held the caliph as a revered figurehead. What Hulagu conquered was a city and a symbol, not the empire of Harun al-Rashid.
The mechanism of the fall combined a vast, methodical war machine with a defender who had neither the force to resist it nor the realism to submit in time. Hulagu had been dispatched from Mongolia with an enormous army and explicit orders to subdue the Islamic heartland. Al-Musta’sim, by contrast, presided over a divided and reduced court, dismissed the danger, refused the Mongols’ demands, and failed to mobilize, even as his armies were destroyed outside the walls. His misjudgment did not cause the disparity of power, but it ensured that the disparity ended in massacre rather than negotiated surrender.
The consequences outlasted the rubble. The killing of the caliph left Sunni Islam without the office that had symbolically united it since the death of the Prophet, and the political shock of an Islamic capital destroyed by non-Muslim conquerors reverberated for generations. The destruction of Baghdad’s books and scholarship became, in later memory, the emblem of a lost golden age — though the city’s intellectual life was not annihilated as totally as legend holds, and libraries reopened within a few years. What was beyond dispute was that an institution more than five centuries old, and the city that had been the center of a world, were broken in a single fortnight.
Between 1219 and 1221, the Khwarazmian Empire of Central Asia — one of the wealthiest states of the Islamic world, spanning much of present-day Iran, Afghanistan, and the lands between the Caspian and the Pamirs — was destroyed by the Mongol armies of Genghis Khan. Its great cities of Bukhara, Samarkand, Gurganj, Merv, and Nishapur were stormed in succession and, in several cases, depopulated; their inhabitants were slaughtered or enslaved in numbers the medieval chroniclers counted in the hundreds of thousands. The empire’s ruler, Shah Ala ad-Din Muhammad II, fled westward and died in destitution on an island in the Caspian Sea around the end of 1220, his realm dissolving behind him.
The campaign is remembered above all for its violence. Where cities resisted or revolted, the Mongols razed them and put the population to the sword; the chroniclers Juvayni and Ibn al-Athir record death tolls at Merv and Nishapur running into the high hundreds of thousands, and while such figures are inflated and debated, the scale of the killing was extraordinary by any measure. A prosperous, irrigated region of millions was reduced, within two years, to a depopulated ruin from which parts of it never recovered. The dead were farmers, weavers, scholars, and townspeople of Khorasan and Transoxiana, and the record of their destruction belongs to them.
The trigger was a diplomatic atrocity. In 1218 the governor of the frontier city of Otrar seized a large Mongol trade caravan, accused its members of spying, and had them killed; when Genghis Khan sent envoys to demand redress, the Shah had one executed and the others humiliated. For a ruler who treated the safety of envoys and merchants as inviolable, this was a casus belli, and the Mongols answered it with annihilation. A quarrel that might have been settled by the surrender of one governor became the destruction of an empire.
Yet the deeper cause lay in the Khwarazmian state itself. It was a recent, overextended creation, its army large but its loyalties fragile, its provinces newly conquered and resentful, and its Shah distrustful of his own commanders. Faced with a faster, better-coordinated enemy, Muhammad II chose to scatter his forces among the cities rather than meet the Mongols in the field — a decision that let them be destroyed one garrison at a time. The empire fell not only because the Mongols were ruthless and disciplined, but because it was brittle, divided, and badly led at the moment of the shock.
On 2 January 1492, Muhammad XII of Granada — known to history as Boabdil — surrendered the city of Granada and the Alhambra to Ferdinand II of Aragon and Isabella I of Castile, the Catholic Monarchs. The Nasrid Emirate of Granada, ruled by its dynasty since around 1238, was the last Muslim state in the Iberian Peninsula; its fall completed the Reconquista, the centuries-long Christian conquest of Iberia, and ended nearly eight hundred years of Muslim political presence that had begun with the invasion of 711. Boabdil handed over the keys and, by the famous account, wept as he left; the symbolic age of Al-Andalus was over.
The conquest was the climax of a ten-year war, fought from 1482 to 1492, in which the combined Castilian and Aragonese crowns ground down a fragmented emirate town by town. Granada’s surrender was negotiated, not stormed: the Treaty of Granada, agreed in November 1491, promised the city’s Muslims their lives, property, laws, mosques, and freedom of worship. Within a decade those guarantees were dismantled. Forced conversions began in 1499 under Cardinal Cisneros; by 1501–1502 Granada’s Muslims faced baptism, exile, or slavery, and the Jews of all Spain had already been expelled by the Alhambra Decree of March 1492. The fall of the state became the prelude to the erasure of its people’s faith.
The emirate fell because it was small, isolated, and divided against itself, confronting a Christian power that had grown larger, richer, and newly unified. The marriage of Ferdinand and Isabella in 1469 had joined Castile and Aragon; Granada, by contrast, was riven by dynastic civil war, with Boabdil, his father, and his uncle fighting one another even as the Christians advanced — a rivalry the Catholic Monarchs exploited with deliberate skill. A state that could not unite against an enemy who could concentrate against it had little chance once the war of attrition began.
Technology and resources decided the rest. The Castilian crown brought a powerful siege artillery train that reduced Granada’s fortified towns far faster than walls had once dictated, and it could outspend and outlast an emirate cut off from any great Muslim power that might relieve it. North African aid never came in strength; Christian Iberia had the men, the guns, and the money, and it applied them methodically. After the fall of Málaga in 1487 and Baza in 1489, the capital stood alone, and its surrender was a matter of time.
The Sasanian Empire — the last pre-Islamic Persian empire, founded by Ardashir I in 224 and ruled from its winter capital at Ctesiphon on the Tigris — was conquered by the Arab Muslim armies of the Rashidun Caliphate between roughly 633 and 651. Its last shah, Yazdegerd III, a grandson of the great king Khosrow II, fled eastward across his own collapsing realm for nearly a decade and was killed near Merv in 651, by tradition murdered by a local miller for the jewellery he carried. With his death the dynasty that had been Rome’s and then Byzantium’s principal rival for four centuries ceased to exist, and Iran began its long passage from Zoroastrian empire to part of the Islamic world.
The empire the Arabs broke was, like Byzantium that same century, already gravely wounded — and the wound was largely self-inflicted. The Sasanian and East Roman empires had fought a final, ruinous war from 602 to 628 in which Khosrow II overran Syria, Palestine, and Egypt before the emperor Heraclius drove deep into Persia and shattered his armies. Both empires emerged exhausted, bankrupt, and depopulated by war and plague. When Khosrow was murdered by his own nobles in 628, the Sasanian state fell into a four-year civil war in which a dozen or more claimants — including two queens, Boran and Azarmidokht — passed across the throne before the nobility agreed on the boy Yazdegerd III in 632.
It was onto this enfeebled, faction-ridden empire, not a Persia at its height, that the Arab armies advanced. The conquest came as a sequence of decisive battles against a state that could no longer absorb a single great defeat. At al-Qadisiyyah, around 636, the Arab commander Sa’d ibn Abi Waqqas destroyed the main Sasanian field army and killed its general Rostam Farrokhzad; Ctesiphon fell soon after; and at Nahavand in 642 — remembered in the Arab tradition as the “Victory of Victories” — the last great Persian army was annihilated. Thereafter the provinces fell one by one as Yazdegerd fled before them.
The consequences were civilizational. Zoroastrianism, the state religion, lost its imperial patronage and dwindled over centuries to a minority faith; Persian elites, language, and administrative genius were absorbed into the new caliphate, which they would in turn reshape; and the lands of Iran, conquered as Arab territory, became over generations a heartland of Islam while retaining a fiercely distinct Persian identity. Few conquests have so thoroughly ended one order and seeded another.