Greek fire was an incendiary weapon used by the Byzantine Empire. The Byzantines typically used it in naval battles to great effect as it could continue burning while floating on water.
It provided a technological advantage, and was responsible for many key Byzantine military victories, most notably the salvation of Constantinople from two Arab sieges, thus securing the Empire’s survival.
The impression made by Greek fire on the European Crusaders was such that the name was applied to any sort of incendiary weapon, including those used by Arabs, the Chinese, and the Mongols. These, however, were different mixtures and not the Byzantine formula, which remained a closely guarded state secret whose composition has now been lost. As a result, to this day its ingredients remain a matter of much speculation and debate, with proposals including naphtha, quicklime, sulphur, and niter.
Incendiary and flaming weapons were used in warfare for centuries prior to the invention of Greek fire. They included a number of sulphur-, petroleum- and bitumen-based mixtures. Incendiary arrows and pots containing combustible substances were used as early as the 9th century BC by the Assyrians, and were extensively used in the Greco-Roman world as well.
Greek fire proper, however, was invented in around 672, and is ascribed by the chronicler Theophanes to the inventor Kallinikos, an architect from Heliopolis in the former province of Phoenice, by then overrun by the Muslim conquests.
The importance placed on Greek fire during the Empire’s struggle against the Arabs would lead to its discovery being ascribed to divine intervention. The Emperor Constantine admonished his son and heir, Romanos II to never reveal the secrets of its construction, as it was “shown and revealed by an angel to the great and holy first Christian emperor Constantine” and that the angel bound him “not to prepare this fire but for Christians, and only in the imperial city”.
As a warning, Constantine added that one official, who was bribed into handing some of it over to the Empire’s enemies, was struck down by a “flame from heaven” as he was about to enter a church. As the latter incident demonstrates, the Byzantines could not avoid capture of their precious secret weapon: the Arabs captured at least one fireship intact in 827, and the Bulgars captured several siphons and much of the substance itself in 812/814. This, however, was not enough to allow their enemies to copy it.
The Arabs employed a variety of incendiary substances similar to the Byzantine weapon, but they were never able to copy the Byzantine method of deployment by siphon, and used catapults and grenades instead.
Greek fire continued to be mentioned during the 12th century, and Anna Komnene gives a vivid description of its use in a – possibly fictional – naval battle against the Pisans in 1099. However, although the use of hastily improvised fireships is mentioned during the 1203 siege of Constantinople by the Fourth Crusade, no report confirms the use of the actual Greek fire, which had apparently fallen out of use, either because its secrets were forgotten, or because the Byzantines had lost access to the areas – the Caucasus and the eastern coast of the Black Sea – where the primary ingredients were to be found.