Greek Fire: Byzantium's Secret Weapon That Burned on Water

It Burned on Water and Couldn't Be Extinguished With Water

In 678 CE, an Arab fleet of several hundred ships besieged Constantinople for the fourth consecutive year and was met with a weapon that Arab chroniclers described with unmistakable terror: a liquid fire projected through bronze siphons onto Arab ships, which clung to wood and water alike and burned intensely even when sailors tried to drown it. The Arab fleet was reportedly destroyed, and the Umayyad Caliphate — at the peak of its western expansion — was forced to sign a thirty-year peace treaty and pay an annual tribute to Byzantium. Greek fire had saved the Eastern Roman Empire.

What Greek Fire Actually Was

The Byzantine weapon was not called "Greek fire" by the Byzantines themselves. They called it "sea fire" (pyr thalassion) or "Roman fire." The term "Greek fire" was applied by Western Europeans who encountered it during the Crusades. The Byzantines guarded the formula with exceptional secrecy — it was reportedly known only to the imperial family and the family of its inventor, Kallinikos of Heliopolis, a refugee from Arab-occupied Syria who brought the weapon to Constantinople around 672 CE.

The formula has never been definitively recovered. The most widely accepted modern hypothesis, advanced by chemist and historian John Haldon and archaeo-chemist Cécile Morrisson, proposes that Greek fire was a petroleum-based mixture — likely derived from crude oil from the Crimea or Caucasus region — combined with quicklime, pine resin, and possibly sulfur. Quicklime (calcium oxide) reacts violently with water, generating intense heat, which would explain the weapon's ability to ignite or intensify on contact with water.

Delivery Systems: Siphons, Grenades, and Hand Pumps

Greek fire was deployed through multiple delivery methods, each suited to different tactical situations.

• Siphon (cheirosiphon): The primary naval weapon — a bronze tube mounted on the prow of Byzantine warships (dromon class), connected to a pressurized container. The mixture was heated and projected through the tube under pressure from a bellows or pump system, creating a stream of fire that could reach 15–20 meters
• Hand-held siphon: A smaller portable version for use on walls and in close combat, operated by one or two soldiers
• Incendiary pots (grenade precursors): Ceramic vessels filled with the mixture and thrown by hand or catapult; some fitted with fuses; others designed to shatter on impact and ignite from contact with air or a small flame
• Fire ships: Unmanned ships loaded with Greek fire and directed toward enemy fleets

The Two Sieges That Defined Byzantine History

Greek fire appeared at two decisive moments that together determined whether the Byzantine Empire would survive at all.

The Arab Sieges of Constantinople (674–678 CE and 717–718 CE): The first siege lasted four years and was repelled with catastrophic losses to the Arab fleet. The second siege, under Caliph Sulayman and later Umar II, involved an Arab force of 1,800 ships and a substantial land army. Byzantine Emperor Leo III deployed Greek fire against the Arab fleet with devastating effect; Arab historian al-Tabari recorded that the Byzantine fire weapons destroyed hundreds of ships in the Golden Horn. Combined with a Bulgarian attack on Arab supply lines, the siege failed. These two failures effectively ended Arab ambitions to conquer Constantinople — a city that finally fell not to Arabs but to Ottoman Turks in 1453.

Attempts to Steal the Formula

The secrecy surrounding Greek fire was maintained for nearly four centuries. Byzantine sources record several attempts by foreign powers to acquire the formula through espionage and bribery. Emperor Constantine VII Porphyrogennetos, writing in the 10th century, explicitly instructed his son never to reveal the composition of "liquid fire" — that it was a gift from an angel to Constantine the Great and could not be shared with foreigners on pain of divine punishment. This instruction appears in the De Administrando Imperio, a confidential manual on statecraft written for the emperor's heir.

• Byzantine soldiers who defected to Arab forces and claimed knowledge of the formula reportedly provided inaccurate information — either through ignorance or deliberate deception
• A 10th-century chronicle records a Byzantine official executed for attempting to sell the formula to Arab agents
• The formula appears to have been lost during the Latin occupation of Constantinople (1204–1261 CE), when the Crusaders who sacked the city did not possess the technical knowledge to maintain production

Greek Fire's Legacy and Modern Parallels

Greek fire represents the first documented use of a sustained liquid incendiary weapon delivered through pressurized mechanical systems — a conceptual precursor to modern flamethrowers (first deployed systematically by Germany in World War I) and napalm (developed in 1942 at Harvard University). The concept of a hydrocarbon-based thickened incendiary that adheres to surfaces and resists water suppression is identical in principle, though different in chemistry. The Byzantine inventors achieved this approximately 1,300 years before the 20th-century versions.