Siege of Constantinople (717-718)
The Second Arab siege of Constantinople (717-718), was a combined land and sea effort by the Arabs to take the capital city of the Byzantine Empire, Constantinople. The Arab ground forces, led by Maslama, were defeated by Constantinople's impregnable walls and Bulgarian attacks while their naval fleet was defeated by Greek Fire and the remnants of it subsequently sunk in a storm on its return home. It is often compared to the more widely studied Battle of Tours in the fact that it halted Islamic expansion into Europe from the East for almost a millenium.
After the first Arab siege of Constantinople (674-678) the Arabs attempted a second decisive attack on the city. An 80,000 strong army led by Maslama, the brother of Caliph Umar II, crossed the Bosporus from Anatolia to besiege Constantinople by land, while a massive fleet of Arab war galleys, estimated to initially number 1,800, sailed into the Sea of Marmara to the south of the city. Emperor Leo III was able to use the famed Walls of Constantinople to his advantage and the Arab army was unable to breach them, whilst the Arab galleys were unable to sail up the Bosporus as they were under constant attack and harassment by the Greek fleet, who used Greek fire to great effect.
Winter and Spring
Constantinople was supplied via the Black Sea and did not suffer much hardship, in contrast to the Arab besiegers on land, who suffered immense losses due to disease and starvation during the winter, as they were not able to supply adequate provisions and were forced to eat their camels, horses, and donkeys. An Egyptian fleet arrived in the spring with fresh reinforcements but successive assaults on the city were unable to cause a breach in its defenses.
The Bulgarians, who had established friendly relations with the Byzantines a year earlier under Khan Tervel, ostensibly because of the looming Arab threat, came to the aid of the besieged city. The Arabs, weary from the long attrition of siege warfare, thinned out by disease and hunger, and demoralized by the lack of success in assaulting the city, were devastated by a Bulgarian attack against their land forces in July. Contemporary chroniclers report at least 30,000 Arabs died in the first Bulgar attack.
Unable to continue the siege in the face of the Bulgarian onslaught and lack of successes, the Arabs were forced to abandon their ambitions on Constantinople in August. Part of the Arab army attempted to withdraw back through Anatolia while the rest attempted to withdraw by sea in the remaining Arab vessels. A devastating storm wracked the Arab fleet on its way back, destroying all but five galleys and drowning the men who had retreated by sea.
This battle was a severe blow to Caliph Umar II and the expansion of the Umayyad Caliphate was severely stunted during his reign. It has macrohistorical importance in that, had Constantinople fallen to this massive force of invaders, the Byzantine Empire most likely would have disintegrated and opened up new opportunities for Islamic expansion into Europe 700 years ahead of the Ottoman invasions. Many contemporary Arab historians look at the Second Arab siege of Constantinople in the same light that Western historians look at the Battle of Tours, as a pivotal milestone in history that turned back the tide of Islamic incursions into Europe, ensuring Christianity would be the dominant religion at a time when Europe was in a state of disarray following the Decline of the Roman Empire.