Greek fire

Στόλος Ρωμαίων πυρπολῶν τὸν τῶν ἐναντίων στόλον, "The Roman fleet burn the opposite fleet down" – A Eastern Roman Empire / Byzantine war ship using their "secret weapon" Greek Fire against a ship belonging to the rebel Thomas the Slav, AD 821. (12th century illustration from the "Madrid Skylitzes").

Greek fire was an incendiary chemical weapon manufactured in and used by the Eastern Roman Empire from the seventh through the fourteenth centuries. The recipe for Greek fire was a closely-guarded state secret, but historians speculate it may have been made by combining pine resin, naphtha, quicklime, calcium phosphide, sulfur, or niter. Roman sailors would toss grenades loaded with Greek fire onto enemy ships or spray it from tubes. Its ability to burn on water made it an effective and destructive naval incendiary weapon, and rival powers tried unsuccessfully to copy the material.