Siege of Constantinople (717–718)

Siege of Constantinople (717–718)
Conflict	Siege of Constantinople (717–718)
Partof	Byzantine–Arab Wars
Date	717–718
Place	Constantinople
Result	Byzantine victory
Combatant1	Byzantine Empire
Combatant2	Umayyad Caliphate
Commander1	Emperor Leo III the Isaurian; Theodotus(quaestor)?; Sergius (patriarch of Constantinople)?; Eutychius (patrikios)?
Commander2	Maslama ibn Abd al-Malik; Caliph Sulayman ibn Abd al-Malik; Caliph Umar II?
Strength1	Estimated garrison, Thematic system troops, naval squadrons
Strength2	Large field army, siege engines, fleet
Casualties1	Heavy but sustainable
Casualties2	Heavy; famine, disease, storms

Siege of Constantinople (717–718) was a pivotal siege in which forces of the Umayyad Caliphate attempted to capture Constantinople, the capital of the Byzantine Empire, from 717 to 718. The siege marked a decisive failure for Umayyad expansion into Balkans and Europe, reinforcing Byzantine resilience under Emperor Leo III the Isaurian and altering the course of the Byzantine–Arab Wars. It involved complex diplomacy with the First Bulgarian Empire, naval confrontations in the Sea of Marmara, and the decisive use of Greek fire.

Background

In the early 8th century tensions rose after Umayyad raids during the reign of Caliph Sulayman ibn Abd al-Malik and Caliph Umar II sought major conquest. The fall of Sicily and pressure on the Anatolian front pushed the Umayyads to plan a major expedition against Constantinople to secure maritime routes and threaten Christendom. Byzantine defensive reforms under preceding emperors such as Justinian II and the development of the theme system shaped the imperial response. Diplomatic maneuvers involved envoys to Khan Tervel of Bulgaria and interactions with Pope Gregory II, reflecting the interconnected politics of Frankish Kingdom and Lombard Kingdom interests in the region.

Forces and Preparations

The Umayyad army assembled under Maslama ibn Abd al-Malik drew veteran units from Syria, Egypt, and Ifriqiya, supported by a large fleet drawn from Alexandria and Cyprus naval resources. Siege engines, including battering rams and siege towers, and logistical convoys were prepared for a long campaign. Byzantium mobilized thematic troops from Anatolikon, Opsikion, Thracesian Theme, and naval squadrons commanded by experienced admirals familiar with Greek fire deployment. Emperor Leo III the Isaurian fortified the Theodosian Walls, stockpiled grain from Thrace and Bithynia, and secured alliances with Khan Tervel of Bulgaria and peripheral principalities. Intelligence networks operating through Constantinople’s chancery tracked Umayyad movements while the imperial court coordinated relief efforts and propaganda to maintain morale among citizens and clergy, including Sergius (patriarch of Constantinople).

The Siege

The Umayyad army reached the outskirts of Constantinople in 717 and established siege lines encircling the city, attempting to blockade the land approaches across the Anatolian sides and control the sea lanes in the Sea of Marmara. Attackers constructed siege engines and conducted assaults against the Golden Gate and the southern walls, while sorties by Byzantine troops harried Umayyad camps. Harsh winter conditions, shortages of fodder, and outbreaks of disease afflicted Maslama’s forces, reducing their operational tempo. Byzantine defenses held, aided by the layered fortifications of the Theodosian Walls, the superior discipline of thematic troops, and persistent counterattacks. Meanwhile, diplomatic pressure and clandestine negotiations with Bulgarian rulers complicated Umayyad supply lines and strategic calculations.

Naval Warfare and Greek Fire

Naval operations were decisive as the Umayyad fleet attempted to enforce a maritime blockade and ferry supplies to the besiegers. Byzantine squadrons, deploying crews from Cappadocia and Pontus, engaged Umayyad ships in the Propontis and near the Golden Horn. The Byzantines’ secret weapon, Greek fire, delivered by specially equipped dromons, inflicted catastrophic losses on Umayyad shipping and lifted the morale of defenders. The maritime victories disrupted the Umayyad logistics chain from Cyprus and Crete and enabled Byzantine resupply missions from friendly ports. Storms in the Marmara and outbreaks of scurvy and dysentery among the besiegers compounded the naval disaster, as recorded in contemporary chronicles associated with Theophanes the Confessor and other annalists.

Relief and Aftermath

By 718, Maslama’s forces, decimated by disease, starvation, and naval losses, began to withdraw; survivors retreated to Syria and Palestine. The effective alliance with Khan Tervel provided Byzantine forces with additional troops and horsemen who harried retreating elements, securing a comprehensive repulse. The failure of the campaign stabilized Byzantine frontiers and contributed to internal shifts in Umayyad strategic priorities, while enhancing Emperor Leo III’s legitimacy and enabling subsequent reforms. The siege’s aftermath saw renewed emphasis on fortification, naval reconstruction, and reorganization of the themes, with long-term implications for Byzantine resilience against Caliphate expansions and for power dynamics with Bulgaria and Khazaria.

Significance and Legacy

The siege represented a turning point in the Byzantine–Arab Wars, halting large-scale Umayyad ambitions toward Central Europe and preserving Constantinople as a Christian stronghold. Its legacy influenced military architecture, naval tactics, and the mythos of imperial salvation linked to leaders such as Leo III the Isaurian and ecclesiastical figures like Patriarch Sergius. Historians and chroniclers including Theophanes the Confessor and later medieval writers debated causes and credit, while modern scholarship examines logistics, Greek fire technology, and the role of climate and disease. The event shaped relationships among Byzantium, the Umayyad Caliphate, First Bulgarian Empire, and neighboring polities, leaving an enduring mark on medieval Eurasian geopolitics.

Category:Sieges of Constantinople Category:Byzantine–Arab Wars