For centuries Byzantium’s seaborne-flank was defended by a fleet of swift galleys; armed with one of history’s greatest secret weapons: Greek Fire!
In 672 three great Muslim fleets were dispatched by the Muslim Caliph, Mu’awiya; to clear the sea lanes and prepare for a Muslim army to besiege the storied capital of the Byzantine Empire: Constantinople. Methodically moving up the Anatolian coast and into the Aegean, they wintered at Smyrna in 673. Entering the Hellespont (Dardanelles) in 674, the Arab armada landed at Cyzicus on the southern shore of the Sea of Marmara. A base was established, and from here the Arab fleets attempted to blockade Constantinople and support the Arab land forces arriving opposite the city, after crossing Anatolia.
This was not the first time the great city had stood siege. Its massive triple walls, constructed during the reign of the emperor Theodosius in the 5th century, had never been breached. However, with command of the sea around the city as well as an army camped outside the walls, the Arabs could cut Constantinople off from outside supply. In time, the great city must surrender or starve.
Finally, in the autumn of 677, the Emperor Constantine IV resolved to confront the Arab besiegers at sea, and break their blockade. His fleet sailed out of the protected anchorage of the Golden Horn, and into the blue waters of the Bosphorus. Wheeling from column into line, the Byzantine fleet darted forth into the open waters of the Sea of Marmara; where the Arab mariners scrambled onto their ships and rowed out to meet them.
The Byzantine galleys were of a type called dromons (“racers”). As the name implies, they were swift galleys, powered by oars and sail. Evolved from the Imperial Roman “bireme”, they differed from the ancient design used by the Greeks and Romans in several key ways. They were either smaller monoremes (powered by a single bank of oars) or biremes (two banks of oars), ranging from 50 to 120 oars. These vessels lacked the distinctive outrigger found in the ancient Greek and Roman galleys (or of the later Renaissance galleys), and the partially-submerged bronze bow-ram that was the main weapon of the ancient warships had been replaced with a sharply pointed bow “spur”; projecting above the water. This was useful in breaking enemy oars, if not in punching a hole in an enemy hull.
The Arab sailors and warriors in the Sea of Marmara that day were sailing ships of the same (or nearly the same) design as the Byzantines; built in Arab-controlled ports in recently captured Egypt and Syria. There, shipyards had built vessels for the Byzantines until those lands were overrun by Muslim armies in the first half of the 7th century; when Islamic forces burst forth from the Arabian Peninsula, filled with religious zeal to spread their faith at the point of the sword. Once in control of former Byzantine ports along the Mediterranean, the Arabs were able to build their own great fleet of dromons to oppose the Byzantines at sea.
Unlike the Arab dromons, though, the main weapon of the swift Byzantine darters sallying forth to offer battle that autumn day was no longer their ship’s beaks, or even their deck-mounted catapults. Instead, siphons and pumping devices were mounted on their bows, and sometimes on gunwale-mounted swivels; devices through which to launch a deadly and highly secret new incendiary weapon: Greek Fire.
The composition of this chemical substance is still unknown. Throughout the centuries that followed that fateful day, it was a secret known only to a few (some historians say only from one-emperor to his successor, though this theory is specious on the face of it); and seems to have disappeared by the 14th century (if not earlier). Contrary to how it has been depicted in some modern recreations, it was neither simply burning oil or merely naptha (though naptha could have been one of the ingredients); but instead a self-igniting composite liquid substance. It had several unique and unusual properties that made it a superb weapon for naval warfare: it burned on water (possibly because quicklime or calcium phosphide were part of the mixture); and, according to some interpretations, was even ignited by water (obviously a chemical reaction). In addition, as numerous writers testify, it could be extinguished only by a few substances, such as sand, vinegar, or old urine (presumably, again, through some chemical reaction).
Greek Fire could be projected through devices (either mounted on the dromon, or hand-held devices carried by crew-members), early forms of modern flamethrowers; or in grenade-like spheres.
Armed with this new “super-weapon”, the Byzantine dromons gave battle to the larger Arab fleet. The details of this decisive battle are lost. All that is known is the outcome: the Arab fleet was defeated and driven from the waters outside the city; and its grand admiral, Yazid ibn Shagara, killed.
The siege was soon broken by a Byzantine victory on land; and the Arab forces, both land and sea withdrew. The Arabs would return again to attempt another siege, with a similar outcome, in 717. Later invaders would meet the same fate at sea, as Byzantine fire dromons defeated fleets of Vikings, Rus, Venetians, and Pisans. The Byzantines also used the weapon to devastating effect during the Bulgarian war of 970–971, when the fire-carrying Byzantine ships blockaded the Danube.
Armed with Greek Fire, the Byzantine Dromon was able to reassert Eastern Roman dominance over the waters of the empire; warding its seaborne flank as ably as the triple walls of Theodosius warded its capital.