13. Greek fire was an ancient flame weapon used by the Byzantine Imperial Navy, resistant to water, but the recipe for which was a guarded secret
“Greek fire” was an incendiary weapon of unknown composition employed by the Byzantine Empire as early as 672 CE. Commonly deployed in naval confrontations, continuing to burn atop the waters rather than being extinguished by them, the flammable liquid was discharged using pressurized nozzles, “siphōns”, akin to the distribution method of a modern-day flamethrower. The discovery of Greek fire was critical to the survival of the Byzantine Empire, with the use of the weapon paramount to the successful defeat of the first and second Arab sieges of Constantinople in 647-678 and 717-718 respectively; Greek fire was also used to great effect by the Imperial Fleet during the Byzantine civil wars, obliterating the opposing ships of Thomas the Slav in 821. However, the weapon also possessed notable limitations, with its successful use depending on favorable winds to direct the flamethrowers.
Despite this recurrent known usage, inspiring “wildfire” in the popular fantasy series Game of Thrones, the precise composition of Greek fire remains uncertain. The formula was a carefully guarded secret of the Byzantine regime, with Emperor Constantine Porphyrogennetos recorded instructing his son, Romanos II, to never reveal the truth as it had been “shown and revealed by an angel to the great and holy first Christian emperor Constantine” for use by “Christians, and only in the imperial city”. Even with the Arab capture of an intact fireship in 827 they were unable to completely reverse engineer the weapon, only able to launch incendiaries by catapult rather than by siphōn.