Greek fire

incendiary weapon used by the Eastern Roman (Byzantine) Empire developed c. 672

Invented by Byzantines, Greek fire was a fearsome weapon. It had the ability to keep burning while on water. As such, it was often used in naval battles. The creation of it was a closely guarded secret and has now been lost.

A Byzantine ship using Greek fire in the late 11th century. Madrid Skylitzes manuscript.

The term "Greek fire" is normally used in English. However, most other languages use other terms such as "sea fire" (Greek: πῦρ θαλάσσιον), "Roman fire" (πῦρ ῥωμαϊκόν), "war fire" (πολεμικὸν πῦρ), "liquid fire" (ὑγρὸν πῦρ), or "processed fire" (πῦρ σκευαστόν).