The Great Wall That Saved a City!

The siege of Constantinople in 717–718 represented the zenith of the Umayyad Caliphate's expansionist ambitions into Anatolia and Southeastern Europe. Following two decades of relentless campaigning that had eroded Byzantine borderlands and depleted its resources, the Caliphate launched its most ambitious assault yet. The Byzantine Empire, meanwhile, was in a state of internal turmoil, with frequent civil wars and disputed successions weakening its central authority and military capacity.

This internal strife created a window of opportunity for the Umayyads, who, under the command of Maslama ibn Abd al-Malik, meticulously planned their invasion. They initially sought to exploit Byzantine divisions, even making common cause with Leo III the Isaurian, a general who was rising against Emperor Theodosius III. However, Leo shrewdly used the Umayyad alliance to secure the imperial throne for himself, turning their expectations of collaboration into a strategic miscalculation.

The invasion force, comprising a massive army and a supporting fleet, crossed into Byzantine territory in 716, setting the stage for a confrontation that would test the very survival of the Eastern Roman Empire.

Constantinople's defense rested on its legendary Theodosian Walls, a formidable triple line of fortifications that had repelled numerous sieges throughout history. These walls, some sections reaching heights comparable to modern skyscrapers, presented a daunting obstacle to the land-based Umayyad army. However, the true turning point in the siege's early stages was the naval engagement.

The Umayyad fleet, essential for a complete blockade, met the Byzantine navy in the Sea of Marmara. Here, the Byzantines deployed their secret weapon: Greek fire. This incendiary liquid, projected through siphons, was devastatingly effective, capable of burning intensely and adhering to enemy ships.

Its use created panic and chaos among the Arab sailors, neutralizing a significant portion of their naval power. This allowed Constantinople to maintain vital sea lanes for resupply, a crucial advantage that sustained the defenders while the besieging army faced increasing hardship and isolation.

As the siege extended into the winter of 717–718, the Umayyad forces found themselves in a dire situation. The harsh, prolonged winter, characterized by heavy snow and extreme cold, was far more severe than anticipated. Coupled with the disruption of their supply lines by the Byzantine navy, the Arab army faced widespread famine and disease.

Morale plummeted as soldiers succumbed to hunger, illness, and the brutal elements. Adding to their woes, the Bulgars, a powerful tribal confederation to the north, launched a series of devastating attacks on the Umayyad rear. This diversionary tactic, likely coordinated or at least opportunistically timed with the Byzantines, stretched the Umayyad forces thin and further disrupted their operations.

The combined pressures of starvation, disease, and attacks from multiple directions created an untenable situation for the besieging army.

By the spring and summer of 718, the Umayyad position had become hopeless. Attempts to reinforce the siege with two additional fleets were met with decisive Byzantine naval victories, further depleting Umayyad naval strength. An overland relief army dispatched through Asia Minor was ambushed and annihilated by Byzantine forces.

Facing complete annihilation, Maslama ibn Abd al-Malik was forced to lift the siege on August 15, 718. The retreat was a catastrophic rout; the remaining Arab fleet was decimated by storms and naval disasters. The failure of the siege had profound and lasting consequences.

It marked the definitive end of the Umayyad Caliphate's large-scale territorial ambitions in Southeastern Europe, effectively halting their westward expansion for centuries. The survival of Constantinople ensured the continuation of the Byzantine Empire as a bulwark against further incursions and preserved a distinct cultural and religious sphere in Eastern Europe. Historians widely regard this siege as one of the most pivotal military engagements in history, fundamentally altering the trajectory of European development and the balance of power between Christendom and the Islamic world.