Greek Fire
Greek fire was an incendiary weapon used by the Byzantine Empire, and it was a devastating weapon. It could burn everything, travel across water and could not be put out. The composition of Greek Fire was a secret, only known to a select few in the military. So strict was the secrecy that the list of ingredients and components were lost over time. Today it’s one of the most enduring mysteries, and a lot of research has gone into figuring out how to recreate it. So far, no luck.