Greek Fire: The Byzantine Empire's Secret Incendiary Weapon

Greek fire was a liquid incendiary weapon used by the Byzantine Empire from the late seventh century, most famously sprayed from bronze tubes on warships to set enemy fleets ablaze. According to Byzantine tradition it was introduced around 672 by Kallinikos, a refugee engineer from Syria, and it played a key part in defending Constantinople against Arab and Rus attacks. Its exact composition was a state secret, and it remains one of the most debated mysteries of medieval technology.

Before Greek fire

Incendiary weapons were not new. Ancient armies had used burning arrows, pots of pitch and sulphur, and simple flamethrowers; the Greek historian Thucydides describes one at the siege of Delium in 424 BC. Romans and Persians used naphtha, a flammable petroleum product found in natural seeps around the Caspian and in Mesopotamia.

What made Greek fire different was the combination of a highly flammable liquid with a system for projecting it under pressure, from a ship, in a controlled stream. That made it a true naval weapon rather than a thrown firebomb.

Kallinikos and the Arab threat

In the mid-seventh century the Arab Muslim conquests swept across Syria, Egypt and North Africa. The Umayyad caliphate built powerful fleets and in the 670s raided the Aegean and attacked the approaches to Constantinople.

The chronicler Theophanes the Confessor, writing in the early ninth century, records that around 672 an architect named Kallinikos fled from Heliopolis in Syria (modern Baalbek in Lebanon) to the Byzantines. He made a “sea fire” which set the Arab ships alight and destroyed them with their crews. Kallinikos was probably a Greek-speaking Christian with knowledge of chemistry and engineering from the Syrian tradition.

The Arab attacks on Constantinople in the 670s were long described as a five- or seven-year siege. Recent scholarship suggests the campaign was smaller and more scattered than later chroniclers claimed. Either way, Greek fire helped the Byzantine navy defeat the Arab fleet, and the Umayyads made peace with Emperor Constantine IV around 678–679.

How the weapon worked

The Byzantines did not call the substance Greek fire. They used names such as “sea fire”, “liquid fire”, “Roman fire” and “prepared fire”. The term Greek fire was coined later by Western Europeans, especially during the Crusades.

On warships, the liquid was projected through a siphon, a bronze tube usually mounted at the bow of a dromon, the standard Byzantine galley. Byzantine military manuals, including the Tactica of Emperor Leo VI (reigned 886–912), describe bronze-covered siphons mounted at the prow; together with other sources, they suggest a system with a pump, a pressurised container and a heated reservoir. The liquid seems to have been heated in a sealed vessel, then forced through a nozzle and ignited as it left the tube, producing a jet of flame aimed at enemy ships.

Leo’s manuals also mention smaller hand-held siphons and clay pots filled with the fire that could be thrown by hand. Princess Anna Komnene, writing in the 12th century, describes how her father Alexios I fitted ships with siphons shaped like the heads of lions and other beasts, so that the flame seemed to come from their mouths, during a sea battle against the Pisans around 1099.

Great victories

Greek fire contributed to several decisive Byzantine victories:

• 717–718: During the great Arab Siege of Constantinople, Emperor Leo III used fire ships against the Umayyad fleet in the Bosporus.
• 821–823: The fleet of the rebel Thomas the Slav was attacked with Greek fire, the scene shown in the illustrated Madrid Skylitzes manuscript.
• 941: A large Rus fleet under Prince Igor of Kiev attacked the region around Constantinople. A hastily assembled squadron of about fifteen old ships fitted with siphons destroyed much of it, according to Byzantine chronicles and the Lombard diplomat Liudprand of Cremona.
• 1043: Another Rus naval attack was repelled with the help of Greek fire.

The Russian Primary Chronicle remembered the terror of the weapon, describing the Greeks as hurling fire that was like lightning from heaven.

The secret

The Byzantines protected Greek fire with extreme care. In the mid-tenth century, Emperor Constantine VII Porphyrogennetos wrote a handbook for his son, known as De Administrando Imperio. In it he instructed that the fire must never be given to any foreign people, explaining that it had been revealed by an angel to Constantine the Great. Anyone who revealed it, he wrote, should face divine punishment.

Knowledge appears to have been confined to particular families of craftsmen and to imperial arsenals. This secrecy succeeded in keeping the weapon out of enemy hands, but it also made the knowledge fragile. If key specialists died, or the supply chain broke down, the art could be lost.

The debate over the formula

No Byzantine recipe for the naval fire survives. Modern scholars have proposed many ingredients:

• Petroleum: Most historians agree that crude oil, or a light fraction of it, was the main component. Oil seeps were known around the Black Sea, especially near Tmutarakan on the Taman peninsula, and in the Caucasus.
• Resins: Pine resin may have been added to thicken the liquid and make it stick to ships. Anna Komnene mentions resin and sulphur for a hand-held incendiary, though this may not be the naval version.
• Quicklime: Older theories suggested quicklime made the fire ignite on contact with water. This is now considered unlikely.
• Saltpetre: Some writers linked Greek fire to gunpowder, but saltpetre was not known in the Mediterranean until the 13th century, long after Greek fire’s introduction. Greek fire was not an explosive.

Experimental reconstructions in the early 21st century, led by the historian John Haldon, showed that heated crude oil forced through a bronze siphon could produce a powerful jet of flame several metres long, consistent with the descriptions. The approach of heating and pressurising the fluid, rather than any single magic ingredient, may have been the key innovation.

This interpretation also explains why the weapon was so hard for enemies to copy. Even if they captured some of the liquid, as the Bulgarians reportedly did in the early ninth century, they would still need the pumps, the heated tanks, the trained operators and a reliable supply of the right oil. Greek fire was a complete system, not just a substance.

Limits, decline and loss

Greek fire was not invincible. It had a short range, probably no more than a few tens of metres, and was best used in calm seas, as wind could blow the flames back onto the Byzantine ship. Handling a heated, pressurised flammable liquid on a wooden galley was dangerous for the crew. Siphon ships were specialised vessels, and the empire seems to have had only a limited number at any time; in 941 the defenders had to refit old hulks because the main fleet was away.

Its effect was often as much psychological as physical. Enemy sailors feared a weapon that could not easily be extinguished and that set the sea itself apparently on fire. Byzantine commanders used that fear, and the reputation of Greek fire may have deterred attacks that never took place.

Neighbouring powers, including the Arabs, developed their own naphtha incendiaries. Muslim armies made wide use of fire weapons during the Crusades, and the crusader chronicler Jean de Joinville later described the terror of incendiary missiles thrown at Louis IX’s army in Egypt in 1249–1250. Westerners called all such weapons Greek fire, which has added to the confusion over what the original Byzantine weapon was.

References to Greek fire become rare after the 12th century. When the armies of the Fourth Crusade attacked Constantinople in 1203–1204, there is no clear evidence that the Byzantines used the classic siphon weapon (see Sack of Constantinople). Whether the formula had been lost, raw materials were no longer available or the specialists had died out is unclear. By the time the city fell in 1453 (see Fall of Constantinople), gunpowder weapons had transformed warfare.

Myths and facts

• Myth: Greek fire was an early form of gunpowder. Fact: It was a burning liquid, not an explosive; gunpowder came from China and spread west centuries later (see Invention of Gunpowder).
• Myth: Greek fire burned underwater. Fact: It floated and kept burning on the water’s surface, which made it hard to put out, but it did not burn beneath the waves.
• Myth: The Greeks of antiquity invented it. Fact: The name refers to medieval Byzantines, whom Western Europeans called Greeks; it dates from the seventh century AD.

Timeline

• 424 BC: A primitive flamethrower is used at the siege of Delium, according to Thucydides.
• c. 672: Kallinikos introduces the “sea fire” to Byzantium.
• c. 678–679: Peace between Constantine IV and the Umayyads after Arab naval defeats.
• 717–718: Greek fire helps defeat the Arab siege of Constantinople.
• 821–823: Greek fire used against the fleet of Thomas the Slav.
• 941: Prince Igor’s Rus fleet is destroyed by Byzantine fire ships.
• c. 950: Constantine VII warns his son never to reveal the secret.
• c. 1099: Alexios I’s fleet uses lion-headed siphons against the Pisans.

Why it matters

Greek fire gave a small and often hard-pressed empire a technological edge at sea for several centuries. It helped Constantinople survive its most dangerous sieges, shaping the history of Europe and the Mediterranean. Its mysterious formula continues to fascinate historians, chemists and the public, making it one of the most famous weapons of the Middle Ages.