Siege of Constantinople

Battle context

The Umayyad siege of Constantinople in 717 was among the most ambitious military undertakings of the Arab–Byzantine wars, deploying a reported 120,000 troops against a Byzantine garrison of 15,000 in an attempt to take the city that served as the intersection of Europe and Asia along the Bosporus, connecting the Sea of Marmara and the Black Sea. Constantinople's position on the Silk Road gave it exceptional strategic value, and its capture would have represented a transformative blow to Byzantine power and a gateway for Umayyad expansion into Europe. The Umayyad Caliphate committed forces under Maslama ibn Abd al-Malik, with backing from the caliphs Sulayman ibn Abd al-Malik and later Umar ibn Abd al-Aziz, alongside commanders including Umar ibn Hubayra and Abdallah al-Battal. The Byzantine defense was organized under Leo III the Isaurian, with support from the Bulgarian ruler Tervel. The campaign ended at enormous cost to the Umayyad side, with recorded losses of 150,000, exceeding the entire initial force — a figure that points to catastrophic attrition over the course of the siege. The failure to take Constantinople preserved Byzantine control of the Bosporus corridor and checked Umayyad expansion westward, marking one of the most consequential repulses of the Arab–Byzantine conflict.