Greek Fire Breaks the Second Arab Siege of Constantinople
A year-long siege ends when a secret weapon and a harsh winter defeat Maslama's army
Quick facts
- Location
- Constantinople
- Byzantine emperor
- Leo III
- Umayyad general
- Maslama
- Decisive weapon
- Greek Fire
What happened
In August 717 CE, shortly after Leo III seized the Byzantine throne, an Umayyad army of about 80,000 men and a fleet of 1,800 ships under the general Maslama besieged Constantinople. The siege dragged on for a year, but the city's fortifications held, and Byzantine ships used the incendiary weapon known as Greek Fire to devastate the Arab fleet. When the Bulgar khan Tervel sent a relieving force to aid Leo, Maslama's army, already weakened by a severe winter, famine, and disease, was forced to withdraw on 15 August 718 CE.
Why it matters
The failed siege halted Umayyad expansion toward Europe's southeastern approach and preserved Constantinople as a Christian capital for another seven centuries, a survival Byzantines commemorated annually afterward. Its failure, alongside the later defeat at Tours, marked the point at which the fastest phase of Islamic territorial expansion into Europe stalled.
How we know
The siege's scale, duration, and outcome are described in the World History Encyclopedia's biography of Leo III, drawing on Byzantine historical sources for the emperor's reign.
Sources
- World History Encyclopedia. Leo III · Reputable sourceworldhistory.org · The domain "worldhistory.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- World History Encyclopedia. Leo III · Reputable sourceworldhistory.org · The domain "worldhistory.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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