Siege of Constantinople (717–718)

A year-long Umayyad campaign against Constantinople, repelled by the Byzantine Empire in 718 through its defenses, naval power, and the attackers’ supply failures.

Theodosian Walls: A massive system of land walls, towers, and moats that protected Constantinople. Their strength helped the city withstand the Umayyad land assault.
Umayyad Caliphate: The first hereditary caliphate, ruling a large empire from Damascus between 661 and 750. It organized the expedition intended to capture the Byzantine capital.
Battle of Akroinon: A Byzantine victory over an Umayyad force in Anatolia in 740. It marked a later phase of Byzantine resistance to Arab expansion after the siege.
Bulgar–Byzantine alliance: A military partnership between the Bulgar state and the Byzantine Empire against common threats. Bulgar forces attacked the Umayyad army during the campaign, worsening its losses.
Greek fire: An incendiary weapon used by Byzantine forces, especially in naval warfare. Byzantine ships used it against the Umayyad fleet in the Bosporus.
Maslama ibn Abd al-Malik: An Umayyad prince and general who commanded the land forces during the siege. His army led the campaign across Anatolia and encamped outside Constantinople.
Second Arab siege of Constantinople: A failed Umayyad naval and land campaign against Constantinople in 654–655, described in some later sources as a siege. It provides an earlier comparison for the strategic limits of attacks on the capital.
Siege of Constantinople (717–718) winter: The winter phase of the 717–718 campaign, when cold and shortages severely weakened the besieging army. Harsh conditions and failing supplies made continued investment of the city increasingly untenable.
Byzantine navy: The naval forces maintained by the Byzantine Empire to defend its coasts and control sea routes. Its attacks disrupted the fleet carrying supplies to the besieging army.
Leo III the Isaurian: Byzantine emperor from 717 to 741 who founded the Isaurian dynasty. He took the throne as the Umayyad army approached and directed the city’s defense.

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