The Battle of Constantinople, 718 A.D. Muslim Invasion into Europe Annihilated, Greek Fire, Land and Sea Battle,Europe Descends into the Dark Ages

With the repulsion of the Muslim forces, Europe’s Christian stronghold remained intact, unchallenged by any significant Muslim threat for centuries — until the fifteenth century’s tides shifted. This triumph, aided by Greek Fire, paired with the Frankish victory at Tours, decisively halted Islam’s advance, confining its western expansion to the shores of the southern Mediterranean.

Constantinople. August 717 - August 718 A.D.
Byzantine Forces: Unknown.
Muslim Forces: 210,000 Soldiers, 2,000 Ships.

Additional Reading and Research:

• Gibbon, Edward. The Decline and Fall of the Roman Empire, Vol 6.
• Fuller, J.F.C. A Military History of the Western World.
• Treadgold, Warren. Byzantium and Its Army.

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Transcript

Hey, thanks for listening to this episode of History's Greatest Battles. If you enjoyed this or any other episode, please subscribe and share it with a friend.  You know, it's not really accepted anymore to refer to Europe's Dark Ages as "the Dark Ages," a period where intellectual stagnation   paralysis was rampant.

Often, I found that people assumed that when Rome fell in the West and the Church took over administration and authority, that it was the dogmatic tendencies of the Church that forced Europe into this period of intellectual starvation that we call the Dark Ages... well, there definitely was a dogmatic rule.

I mean, look at the Inquisitions throughout history. Not just the famous Spanish Inquisition, but the hunting of anything heretical that might affect authority.   In reality, what occurred in the Dark Ages was knowledge that was once in Europe was forgotten. Europe had built a defensive wall, per se, around itself.

And while it allowed the power players to maintain their authority, there was a period of horrific stagnation, culturally and intellectually. We can trace the true moment of this conception, this Dark Age conception, to today's battle. Let's experience now the Battle of Constantinople. 

Welcome to History's Greatest Battles, Season 01, episode 43: The Battle of Constantinople, August of 717 to August of 718.

Byzantine Christian Forces: Unknown.

Muslim Forces: 210,000 soldiers.

With the repulsion of the Muslim forces, Europe’s Christian stronghold remained intact, unchallenged by any significant Muslim threat for centuries—until the fifteenth century’s tides shifted. This triumph, paired with the Frankish victory at Tours, decisively halted Islam’s advance, confining its western expansion to the shores of the southern Mediterranean.

For ten relentless years, from 622 to 632, Mohammed the Prophet strode across the Arabian sands, reshaping the destiny of a people and carving the path of Islam with unwavering conviction. When death finally claimed the Prophet, no clear heir stood before the swelling tide of the faithful, but it was Abu Bakr, his steadfast ally, who was thrust into the role of successor by those closest to the heart of the movement. Abu Bakr’s reign was brief, a mere two years, but in that short span, he wielded authority like a blade, unifying a nascent empire that threatened to fracture under its own weight.

After Abu Bakr’s passing, the mantle of caliphate fell upon Omar, a man of iron will, who now stood as both the spiritual and political helm of the burgeoning Islamic empire. For a full decade, Omar commanded the Islamic armies with ruthless efficiency, driving their conquests deep into Byzantine lands, across Persia’s ancient plains, through Syria’s deserts, and into the very heart of Egypt, shaping an empire that now reached far beyond the Arabian Peninsula. Under the caliphate of Othman, the Islamic tide surged even further, washing up against the Atlantic coasts of North Africa and crashing against the eastern mountains of Armenia and Afghanistan. His leadership stretched Islam’s grasp to its greatest reach yet.

Othman’s rule was cut short by an assassin’s blade, and with his death, Islam itself was cleaved in two. On one side, the followers of Mohammed’s bloodline rallied behind his nephew Ali, giving birth to the Shiite cause. On the other, the power-hungry governor of Syria, Muawiya, rose, and the Sunni faction was born. Muawiya, relentless and cunning, seized control and founded the Umayyad dynasty, anchoring his empire in Damascus, where he ruled with an iron fist from 661 to 750, ensuring the dominance of his lineage over the Islamic world.

Muawiya’s gaze fixed on the Christian Byzantine Empire, driven by a singular, ruthless ambition: the fall of Constantinople. The prize was not just the city itself, but divine absolution—whispers claimed that whoever brought the city to its knees would see their sins washed away. Between 674 and 678, Muslim forces hurled themselves against Constantinople’s defenses, surging by land and sea, yet the city’s impregnable double walls stood like a fortress of stone and will, defying every assault. With his forces bloodied and spent, Muawiya begrudgingly bent to the Byzantine emperor’s terms, signing a peace that demanded a humiliating tribute from Damascus to Constantinople each year, a bitter reminder of his defeat.

Over the next three decades, Islam’s armies swept forward, bearing the banner of faith from the far reaches of Spain to the distant frontiers of India. Yet, no matter how far they marched, Constantinople—the very gateway to Europe—remained an ever-present temptation. Caliph Walid, a master of preparation, amassed the legions and ships to finally claim Constantinople, but death seized him before he could see the siege begin, leaving his dream unfulfilled. Upon Walid’s death, his successor, Suleiman, wasted no time, unleashing an armada and a host of men toward Constantinople in 717, determined to achieve what his predecessor could not.

The Byzantine Empire, beleaguered and weakened by a string of incompetent emperors, had barely recovered from the wounds of past assaults. As the Muslim armies gathered like a storm, it was Emperor Anastasius who wore the imperial crown, his reign ill-prepared for the ferocity about to descend upon him. Ascending to the throne in 713, Anastasius scoured his empire for men of strength and skill, desperate to find warriors capable of defending a realm on the brink of destruction. Among his ranks was a man of grit and cunning, a general named Conon, though history would remember him as Leo the Isaurian.

Leo had served the empire since 705, his loyalty forged in battle, and by 716 he was entrusted with the command of Anatolia, a crucial region standing as a bulwark against the Muslim advance. As Muslim forces surged out of Syria, Leo harried them with guerrilla tactics, wearing down their advance before he turned his sights on the throne itself, wresting it from Anastasius in March 717. Crowned as Leo III, he wasted no time. He fortified the city with provisions for the half-million souls within its walls, preparing for the inevitable siege that loomed on the horizon, knowing full well the scale of the challenge before him. With relentless focus, Leo directed the repair and reinforcement of Constantinople’s towering double walls, positioning siege engines and deadly weapons to crush any assault from either land or sea.

Caliph Suleiman entrusted his brother, Muslama, with command, unleashing an army of 80,000 soldiers that thundered through Anatolia, their eyes set on the impregnable walls of Constantinople. Muslama’s strategy was to suffocate Constantinople from the landward side, while a formidable Muslim fleet cut off all supplies, tightening a naval noose around the city's lifeline. A vast fleet of 1,800 ships, bristling with 80,000 more warriors, sailed under the command of another general, Suleiman, whose name echoed that of the caliph but carried its own weight in the annals of war.

The fleet divided with precision: one arm locking down the Dardanelles, sealing Constantinople from Mediterranean aid, while the other tightened its grip on the Bosporus, cutting off any hope of relief from the Black Sea. In July 717, Muslama marched his army across the Hellespont, dividing his forces with ruthless efficiency. He led the main siege, but sent a detachment to Adrianople to guard against the unpredictable Bulgars, who had sacked Constantinople just five years earlier.

Muslama wasted no time, launching a ferocious assault on the walls the moment his army arrived, but the city’s defenses swatted away his forces with ease, the strength of the fortifications evident from the outset. The failure of his initial attack made one thing clear: a direct assault would only lead to slaughter. Muslama shifted his tactics, ordering his men to dig deep trenches, caging the city and ensuring none could escape. With the land assault stalled, the true battle shifted to the sea, where the fate of the city would now be decided.

General Suleiman, following his orders with military precision, stationed a portion of his fleet at the Dardanelles while leading the rest northward to blockade the Hellespont, tightening the siege from the sea. But as Suleiman’s ships neared Constantinople, the waters betrayed them. Unfamiliar and swift currents tangled the leading vessels, sowing chaos in the heart of his fleet. Leo, ever vigilant, seized the moment. With lightning speed, he lowered the massive chain guarding the Golden Horn and unleashed his fleet, striking before the Muslim ships could even form a battle line.

Armed with the devastating power of Greek fire, Leo’s ships turned the Muslim fleet into a burning graveyard, engulfing vessel after vessel in flame. The surviving ships scattered in retreat, terrified by the inferno. Suleiman, shaken by the ferocity of Leo’s assault, dared not risk his remaining ships. One more strike could obliterate his entire naval force. For now, the northern supply route remained open, a vital artery through which the city’s defenders could still draw breath.

The siege was already faltering, but worse news came from Damascus. Caliph Suleiman had succumbed to a stomach ailment, perhaps from overindulgence, and in his place rose Omar II, a man far removed from the battlefield and lacking the tactical prowess to salvage the campaign. The siege ground on for months in a bleak stalemate, the monotony of war and starvation weighing on both sides, as the bitter stand-off dragged into the winter. But fate had yet more cruelty in store for the Muslim forces that winter.

The winter of 717-718 descended with a vengeance, colder than any in living memory. Snow blanketed the ground for over three brutal months, a white shroud choking the land. For the men of Arabia and Egypt, unaccustomed to the biting cold, it was a nightmare. Discomfort quickly turned to despair, and then to death, as the harsh climate exacted its toll. With supply lines frozen and delayed by the merciless weather, starvation and sickness ravaged the Muslim camp. Thousands of soldiers succumbed to the elements, their bodies littering the frozen ground in silent testament to their suffering.

Spring of 718 was meant to bring hope for the Muslim army. A new fleet from Egypt, bolstered by 50,000 fresh reinforcements, was poised to reignite the campaign. Under cover of night, 400 ships from Egypt slipped past the Byzantine fleet guarding the Golden Horn, avoiding confrontation and establishing a menacing presence at the Hellespont, poised to tighten the siege’s grip. With the supply routes severed, Constantinople’s fate seemed sealed, yet once more, Leo’s navy emerged to shatter the encroaching noose, turning the tide of battle.

Leo’s victory was hastened by an unexpected windfall—large numbers of Coptic Christians aboard the Egyptian fleet, forced into service, defected en masse, further crippling the Muslim war effort. Seizing this moment of disarray, Leo struck in June with a sudden, vicious attack. The Muslim fleet, caught entirely off guard, was thrown into chaos. The infernal Greek fire roared to life once again, unleashing both destruction and terror. The remaining Christian crews abandoned their posts, flocking to Leo’s side in droves, leaving the Muslim fleet in flames.

With the northern blockade crushed, Leo followed his triumph with a swift, deadly strike across the Sea of Marmara, where Muslim forces on the Asian shore were decimated before they could react. The attack hit like a hammer blow, catching the defenders completely off-guard. Thousands were slaughtered where they stood, their defenses crumbling in the face of Leo’s ruthless onslaught.

Leo, as cunning in diplomacy as he was fierce in battle, dispatched envoys to the Bulgar king, Tervel. His words, sharp as his swords, convinced Tervel to strike the Muslim forces from the west, turning a potential adversary into a brutal ally. In July, Tervel’s Bulgar warriors swept down like a storm, smashing through the Muslim holding force near Adrianople and delivering a devastating blow to Muslama’s rear. By the time their fury was spent, 22,000 Muslim soldiers lay dead.

As if Tervel’s onslaught wasn’t enough, a new rumor spread through the Muslim ranks like wildfire—the Franks, feared for their military prowess, were said to be marching across Europe to join their Christian brethren in defense of Constantinople. Though the Muslims had never faced the Franks in battle, they had heard tales of their strength, and those stories now fanned the flames of fear within their ranks. The specter of a Frankish army, combined with the relentless Bulgarian assault, was too much for Caliph Omar to bear. On August 15, 718, he ordered Muslama to withdraw, and the battered Muslim army finally retreated from the shadow of Constantinople’s indomitable walls.

Among the enduring enigmas of the ancient world is the fearsome substance known as Greek fire, a weapon whose secrets have remained locked away for centuries. Though its origins trace back to the time of Archimedes and the Peloponnesian War, Greek fire surfaced sporadically across a thousand years of naval and siege warfare, striking terror whenever its flames appeared. Guarded jealously by those who wielded its power, the recipe for Greek fire has never been uncovered. Despite centuries of warfare, no leak, no record, not even a fragment of its formula has survived to reveal its mysteries to modern scholars. Perhaps the most insightful analysis of Greek fire resides in Edward Gibbon’s monumental work, The Decline and Fall of the Roman Empire, vol. 6:

“The historian who presumes to analyze this extraordinary composition should suspect his own ignorance and that of his Byzantine guides, so prone to the marvelous, so careless, and in this instance so jealous, of the truth. From their obscure and perhaps fallacious hints, it should seem that the principal ingredient of the Greek fire was the naphtha, or liquid bitumen, a light, tenacious, and inflammable oil which springs from the earth and catches fire as soon as it comes in contact with the air. The naphtha was mingled, I know not by what methods or in what proportions, with sulphur and with the pitch that is extracted from evergreen firs. From this mixture, which produced a thick smoke and a loud explosion, proceeded a fierce and obstinate flame, which not only rose in perpendicular ascent, but likewise burnt with equal vehemence in descent or lateral progress; instead of being extinguished, it was nourished and quickened by the element of water; and sand, urine, or vinegar were the only remedies that could damp the fury of this powerful agent, which was justly denominated by the Greeks the liquid or the maritime fire. For the annoyance of the enemy, it was employed with equal effect by sea and land, in battles or in sieges. It was hurled from the ramparts in great boilers, or launched in red-hot balls of stone and iron, or wrapped around arrows twisted with flax and tow, deeply soaked in the deadly, inflammable oil: sometimes it was delivered through instruments of even greater vengeance, blasted through long copper tubes mounted on the prows of war galleys, fashioned into the terrifying jaws of monstrous beasts, spewing liquid flame that consumed all in its path. This fearsome art was guarded in Constantinople as the empire’s most precious secret. The galleys and artillery might sometimes be shared with Rome’s allies, but the composition of Greek fire was hidden behind walls of secrecy, protected with fanatical vigilance, and the terror it spread among enemies was magnified by their utter ignorance of its nature, each encounter a deadly surprise. In the Administration of the Empire, the royal author, [Constantin], laid out careful strategies to deflect the prying curiosity and desperate demands of foreign rulers, anxious to uncover its secrets. They were to be told that the secret of Greek fire had been divinely granted by an angel to the first and mightiest Constantine, with the holy command that this gift of heaven, this unique blessing of Rome, should never be shared with any foreign nation; that both prince and subject were bound by sacred silence, under threat of the most severe temporal and spiritual punishments for treason and sacrilege; and that any impious attempt to uncover its secrets would unleash the swift and supernatural wrath of the Christian God. Through these precautions, the secret remained confined to the Romans of the East for over four centuries; and even by the end of the eleventh century, the Pisans—masters of every sea and art—could only endure the deadly effects of Greek fire, never grasping its true composition.”

The defeat at Constantinople was Islam’s first great catastrophe, a devastating blow unlike anything their armies had faced before. Though they had suffered defeats in isolated battles, never had they endured such a crushing, all-encompassing disaster. Out of the colossal force of 210,000 that descended upon Constantinople, only 30,000 souls lived to return home, leaving behind a shattered army on foreign soil. The fleet that once boasted over 2,000 ships was reduced to ruin, with a mere 5 vessels limping back to port—a ghostly reminder of the navy’s once-mighty presence.

Had Muslama’s legions breached Constantinople’s defenses, the gates of eastern Europe would have swung wide open, unguarded and vulnerable to the tide of Islamic conquest. With no force standing in their way until the distant armies of western Europe, there would have been little organized resistance strong enough to stem the flood of Muslim warriors pouring across the continent. Constantinople, the beating heart of Christian power in the East—political, religious, and economic—would have likely become the new center of Islam, changing the balance of faith and power forever. The Eastern Orthodox Church might have vanished, swept away by the tide, with unimaginable consequences rippling through eastern Europe and Russia, reshaping the spiritual landscape.

Naval supremacy would have been claimed entirely by the forces of Islam, as no European nation could yet muster a fleet capable of contesting them—a void that would not be filled until the Viking longships prowled the seas nearly a century later. Even the Frankish triumph at Tours, just 15 years later, might not have been enough to stop the tide, leaving Islam poised to become the dominant faith of Europe, and potentially the world. Yet history took a different course. Islam’s power remained formidable, but its influence stayed distant, its advance checked at the walls of Constantinople.

The rapid spread of Islam through Byzantine lands in the Middle East unnerved both emperors and church leaders, as countless subjects welcomed their new conquerors without resistance. Byzantine rule had earned a reputation for its oppressive taxation and rigid enforcement of Orthodox doctrine, leaving many under its control disillusioned and eager for change. To those under Byzantine rule, Islam presented a more tolerable alternative, offering religious freedom, and even the taxes imposed on non-Muslims were lighter than the burdens extracted by Constantinople. Yet the spread of Islam posed an existential threat, forcing the Orthodox Church to make uneasy concessions, reshaping itself in an attempt to appeal to Muslim sensibilities.

This shift manifested in the rise of iconoclasm, a sweeping movement that rejected the use of religious images and icons in worship, mirroring Islamic teachings. Islam forbade all pictorial representations of life, viewing them as an affront to the ultimate authority of God as Creator. The Orthodox Church, for a time, followed suit, banning icons from worship, a move that sparked a deep rift with the Roman Catholic Church. In Europe, where literacy was sparse, the Church relied heavily on icons to convey religious teachings to the masses, making their removal an untenable prospect. This deepened the ever-growing rivalry between the two religious centers, Rome and Constantinople, sharpening the divide within Christendom. It would not be until the twelfth century, during the fire and blood of the Crusades, that any significant cooperation between these factions would emerge.

The Byzantine victory may have shielded Europe from Islam’s reach, but it also closed Europe off from nearly all external influences, entrenching it in isolation. While the wisdom of Hellenistic culture endured and thrived in the Middle East and Africa, Europe slipped into the shadows of the Dark Ages, a period defined by cultural and intellectual stagnation. Though Europe could fend off invasion with military might, cultural progress crawled at a glacial pace, hindered by its self-imposed isolation. Only with the Crusades and the revival of trade with the East did Europe begin to reclaim the lost treasures of ancient knowledge, sparking the dawn of the Renaissance and a new era of enlightenment. One can only wonder how drastically the fate of Europe might have changed had Constantinople fallen in 718 rather than in 1453, altering the very course of civilization itself.