Share This Article

The 632 death of Muhammad, the unifying Arab military leader and founder of Islam, presaged the beginning of the Muslim conquests that overran much of the Middle East and North Africa. By the early 8th century Muslim armies of the Umayyad caliphate stood poised on Europe’s doorstep, with the Byzantine capital of Constantinople as their primary obstacle.

In 717 the Umayyad Caliph Sulayman, looking to kick open the door to the Continent, sent his brother Maslama against Constantinople with an army of at least 80,000 men and a fleet of some 1,800 galleys. Facing them were a vastly outnumbered garrison and small navy.

Somewhat balancing the scales, however, was a secret weapon—Greek fire—not to mention Leo III the Isaurian, arguably the Byzantines’ greatest warrior-emperor. Recognizing the threat well in advance, the Byzantines had prepared by stockpiling food and supplies, and Leo used his diplomatic skills, and a great deal of Byzantine gold, to secure the aid of a large Bulgar army from outside Constantinople.

The defenders repulsed initial Muslim attempts to take the city via the inlet known as the Golden Horn, as Byzantine light galleys called dromons (“runners”) rammed the Umayyad ships and set their decks ablaze with Greek fire—an early form of napalm that burned on water and could be extinguished only by sand or urine. Subsequent Muslim incursions met similar fates.

Despite receiving reinforcements from Egypt and Africa, the Muslim army made no headway and finally lifted its yearlong siege after losing 22,000 men to the Bulgars at Adrianople.

Historians often credit Frankish commander Charles Martel’s celebrated victory at Tours in 752 with stopping the Muslim advance into Europe, but the force Martel faced—with far more troops at his command—was one-quarter the size of the army Leo had defeated. Leo’s victory is all the more notable in that it occurred when the Continent was in the throes of the Dark Ages and comprised mainly small, quarrelsome kingdoms that would have stood little chance of turning back the Muslim host.


The enemy of my enemy can be an ally. The Bulgars were never fast friends of the Byzantines, but a standing treaty coupled with Leo’s successful persuasion (and overt bribery) of their khan, Tervel—a fellow Christian who would fight for his faith—was decisive in breaking the siege.

Technology can give you an edge. The effective use of Greek fire enabled the Byzantines to neutralize the Umay- yad fleet as a fighting force.

Pick the right man for the job. Leo’s predecessor, Theodosius III, was more monk than commander and, indeed, ceded his throne to enter a monastery. Leo was by training and disposition a warrior whose organizational and tactical skills preserved Constantinople.

Plan ahead. The Byzantines had stored ample food and supplies for the siege, while the Muslims, unprepared for a harsh winter, died in droves from exposure, starvation and disease.

Know your strengths. Leo knew the double walls of Constantinople could withstand virtually any assault by land. Realizing the Muslims would rely on a seaborne attack, he concentrated on defending the Golden Horn with his nimble galleys spewing Greek fire.

Understand the consequences. Had the Muslims taken Constantinople in 717 instead of seven centuries later, Islam might have gobbled up Europe unopposed.