Greek fire was a powerful Byzantine incendiary weapon that was a closely guarded military secret. Its true composition remains unknown to this day, despite multiple theories.
Greek fire was first used by the Byzantine Emperor Leon III's army, when enemy vessels laid siege to Constantinople in the year 717. In the battle, the napalm-like substance burned through the enemy fleet, forcing them to call off their attack and flee west. 
In 1511, the Assassin Ezio Auditore da Firenze used Greek fire in order to destroy several ships, which prevented him from leaving the city. The Ottoman Assassins also mounted Greek fire weapons along the barricades they used to defend their dens from Templar attacks.
- In the novelization of Assassin's Creed: Brotherhood, the defenders used Greek fire during the Siege of Viana.
- Greek fire is referenced in Assassin's Creed: Origins, during a side memory; in 47 BCE, the Medjay Bayek of Siwa is tasked by the architect Vitruvius to destroy the reserves of "a Greek Fire of sorts" that the Roman General Agrippa had had manufactured.
- In the DLC of Assassin's Creed: Odyssey, Legacy of the First Blade, a flamethrower weapon akin to Greek fire called Chimera's Breath was introduced.
- Assassin's Creed: Brotherhood novel (first appearance)
- Assassin's Creed: Revelations
- Assassin's Creed: Origins