Any of several flammable mixtures used in ancient and medieval warfare, particularly a petroleum-based mixture invented by the Byzantine Greeks in the 7th century. Flammable materials such as pitch and sulfur had been used in war since ancient times, but true Greek fire was especially deadly. Thrown in pots or discharged from tubes, it apparently caught fire spontaneously, and water could not put it out. Greek fire launched from tubes mounted on ship prows wrought havoc on the Arab fleet attacking Constantinople in 673. Its effectiveness was a prime reason for the long survival of the Byzantine Empire. The recipe was so secret that its precise composition remains unknown.