Greek fire

For four centuries a liquid that burned on water kept Constantinople safe, and the recipe died with the people who knew it.

Greek Fire, an Imperial Secret and the Formula That Died

Greek fire was the Byzantine Empire's liquid incendiary weapon, developed around 672, first used against the Arab siege that followed, and sprayed from tubes called siphons on warships. It helped save Constantinople from two Arab sieges. Emperor Constantine VII told his son to tell foreigners it had been revealed by an angel and must never be shared, and its exact formula was lost. Here are the sources, the modern reconstructions, and what is still unknown.