Greek Fire

Greek fire is a weapon used by the gods and Demigods, and is described by Percy as being "one of the most dangerous magical substances in the world". It burns like green fire and can be made into bombs. Hephaestus' cabin used it during chariot races in The Sea of Monsters. Greek fire was also used to fend off the forces of Kronos who were invading the camp from the Labyrinth. Charles Beckendorf used Greek fire to blow up the Princess Andromeda in The Last Olympian, in order to slow down Kronos on his invasion of Mount Olympus. Percy escaped, but Beckendorf sacrificed himself. Later in The Last Olympian, the Hephaestus campers used Greek fire to defend the Holland Tunnel during the Battle of Manhattan. Greek fire can also burn underwater shown in The Last Olympian when Percy goes to Poseidon's underwater palace. Greek fire is described as a swirling green liquid that explodes if dropped on the ground, and the container is broken. It is also used as a decoration for Hades' cabin at Camp Half-blood.

Greek fire was an actual weapon used by the mortals of the Byzantine Empire, which controlled Greece between the Romans and the Turks. How it was made is a lost secret. Although the term "Greek fire" has been general in English and most other languages since the Crusades, in the original Byzantine sources it is called by a variety of names, such as "sea fire" (Greek: πῦρ θαλάσσιον), "Roman fire" (πῦρ ῥωμαϊκόν), "war fire" (πολεμικὸν πῦρ), "liquid fire" (ὑγρὸν πῦρ), or "processed fire" (πῦρ σκευαστόν).[2