Greek fire was a devastating incendiary weapon used by the Byzantine Empire to defend themselves against their enemies.
Greek Fire became the most potent weapon of Christendom for over 700 years. Greek Fire became so important to the Byzantines that Emperor Romanos II (reigned 959-963 AD) declared that three things must never reach enemy hands: the Byzantine imperial regalia, any royal princess, and Greek Fire.
Greek fire was created in the mid to late seventh century in Constantinople by the Syrian architect Kallinikos. The exact chemical makeup of the weapon is unknown however, the fact that water is unable to extinguish it leads some to speculate that the active ingredient was calcium phosphide – made by heating lime, bones, and charcoal. On contact with water, calcium phosphide releases Phosphine, which ignites spontaneously actually making the weapon equally dangerous, if not more so, on water as it is on land.
Because of its effectiveness on water the first use was by the Byzantine Navy. There are a few ways the navy would implement the weapon. First was by firing a ball wrapped with cloth that was doused with the compound and lit on fire onto the other ships probably from a small catapult. Also, some ships were able to pump the compound directly onto the other ship and then ignite it. Greek fire was so effective at sea that it would continue to burn even under water.