Greek fire

Greek Fire, (Greek: Υγρό Πυρ, meaning "liquid fire") was an incendiary weapon available in Constantinople.

History
First used by Byzantine Emperor Leon III's army when enemy vessels laid siege to Constantinople in 717 AD, Greek Fire burned through the enemy fleet, forcing them to lift their attack and travel west.

In 1511, the Assassin Ezio Auditore da Firenze used the flammable substance in order to destroy several ships in the port that prevented him from leaving the city.

Greek Fire was a closely guarded military secret. Its composition remains unknown, despite multiple theories.

Trivia

 * Greek Fire was first seen in the E3 Gameplay Demo of Assassin's Creed: Revelations. Its concept appears similar to the Naval Cannon featured in Assassin's Creed: Brotherhood.
 * Greek Fire can be put in Assassin Dens on barricades in order to counter a Byzantine Templar attack on a den.