Greek fire was an incendiary weapon used by the Byzantine Empire in c. 672.
Used to set light to enemy ships, it consisted of a combustible compound emitted by a flame-throwing weapon.
Some historians believe it could be ignited on contact with water, and was probably based on naphtha and quicklime.
The Byzantines typically used it in naval battles to great effect, as it could supposedly continue burning while floating on water.
The technological advantage it provided was responsible for many key Byzantine military victories, most notably the salvation of Constantinople from the first and second Arab sieges, thus securing the Empire's survival.
The inventor of the legendary weapon, Greek fire, was actually a Graeco-Syrian named Kallinikos. He was born in Heliopolis, modern day Baalbak in Lebanon. Greek fire was developed against the Arab fleet that threatened the empire.
The composition remains a matter of speculation and debate, with various proposals including combinations of pine resin, naphtha, quicklime, calcium phosphide, sulfur, or niter.