Combustion Chemistry & Thermodynamics

Greek Fire

The secret weapon of Byzantium — combustion chemistry, flamethrowers, and the original weapons mystery.

Combustion Chemistry & Thermodynamics12-Month Curriculum 12h

The Story

The Burning Sea

In the summer of 678 CE, the Arab fleet — the most powerful navy in the world — sailed through the Sea of Marmara toward Constantinople, the capital of the Byzantine Empire. The fleet carried thousands of soldiers. The city's walls had never been breached by sea. But the Arabs had a plan: they would blockade the city, starve it, and force a surrender.

They never got the chance.

As the Arab ships approached the sea walls, Byzantine warships — small, fast dromons — raced out to meet them. Mounted on the prow of each dromon was a device that looked like a bronze lion's head with its mouth open. From that mouth came a jet of liquid fire — a stream of burning fluid that arced through the air and splashed across the Arab ships.

The fire stuck to everything it touched. It could not be put out with water. In fact, water made it burn harder. It floated on the surface of the sea, turning the water itself into a burning field. Sailors who jumped overboard to escape burning ships found themselves swimming through fire.

The Arab fleet was destroyed. The siege was broken. Constantinople would survive for another 775 years.

The weapon was called Greek Fire, and it was the most closely guarded military secret in the ancient world.

What Was It?

We don't know. And that's not a failure of modern chemistry — it's a testament to how well the Byzantines kept their secret.

The recipe for Greek Fire was known only to the Kallinikos family — its inventors — and the reigning Emperor. It was passed down through generations under an oath of secrecy. When the Byzantine Empire finally fell in 1453, the secret died with it.

What we do know, from contemporary descriptions and modern chemical analysis of residues, is that Greek Fire had several extraordinary properties:

1. It burned on water. This rules out any purely alcohol-based or oil-based incendiary. Ordinary oil floats and burns on water, but it can be smothered or diluted.

2. Water intensified the burning. This suggests a component that reacts exothermically with water — meaning the reaction with water produces heat, which feeds the fire.

3. It was projected as a liquid stream from pressurized siphons, like a modern flamethrower.

4. It adhered to surfaces — hulls, sails, skin — and could not be easily scraped off.

Modern chemists have proposed several candidate recipes. The most widely accepted theory is that Greek Fire was based on crude petroleum (naphtha), thickened with pine resin to make it sticky, and possibly combined with quicklime (calcium oxide) — a substance that reacts violently with water, producing intense heat.

The Chemistry of Combustion

To understand Greek Fire, you need to understand combustion — the chemical reaction that produces fire.

Combustion is an exothermic oxidation reaction. A fuel (a substance containing carbon and hydrogen) reacts with oxygen, producing carbon dioxide, water, and energy in the form of heat and light:

Fuel + O₂ → CO₂ + H₂O + Energy

The key requirement is the fire triangle: fuel, oxygen, and heat. Remove any one, and the fire goes out.

Ordinary fires can be extinguished by removing oxygen (smothering with a blanket), removing heat (pouring water), or removing fuel (creating a firebreak). Greek Fire was terrifying because none of these methods worked:

- Water didn't cool it — the quicklime reacted with water exothermically, adding heat. - Smothering didn't work because the naphtha was liquid and spread across any surface that tried to cover it. - Removing fuel was impossible because the sticky resin adhered to whatever it touched.

Quicklime and Water

The reaction between quicklime and water is one of the most dramatic in everyday chemistry:

CaO + H₂O → Ca(OH)₂ + Heat (65 kJ/mol)

Calcium oxide (quicklime) reacts with water to produce calcium hydroxide (slaked lime) and a large amount of heat — enough to raise the temperature of the surrounding material above the flash point of naphtha, reigniting any fire that water might have temporarily cooled.

This reaction is so energetic that quicklime was used for centuries as a heat source in situations where fire was impractical. During World War I, soldiers heated their food using cans of quicklime activated by water. Today, self-heating coffee cans and military ration heaters use the same chemistry.

The Siphon

The delivery system was as remarkable as the fuel. The Byzantines projected Greek Fire through bronze tubes using air pressure — essentially a pump-action flamethrower.

The mechanism was a force pump (similar to a bicycle pump) connected to a heated, pressurized tank of Greek Fire. A fire was kept burning beneath the tank to keep the mixture liquid and to increase the internal pressure. When the operator worked the pump lever, pressurized air forced the liquid through a narrow bronze nozzle, creating a jet that could reach 15 to 20 metres.

The nozzle was often shaped like an animal's head — a lion, a dragon, a serpent — both for psychological effect and because the narrow throat of the animal shape created a natural nozzle that accelerated the liquid stream, increasing its range.

The Mystery Endures

Despite centuries of research, no one has conclusively recreated Greek Fire. Several teams have come close — producing sticky, water-resistant incendiary mixtures based on naphtha and quicklime — but none has matched all the described properties simultaneously.

The mystery is part of the lesson. Greek Fire teaches us that chemistry is power — and that the people who understood combustion, pressure, and chemical reactions 1,300 years ago wielded that understanding as effectively as any modern weapons engineer.

It also teaches us something about secrets: the Byzantines kept this one for 800 years. In an age of instant information, it's worth remembering that the most powerful technology in the medieval world was protected not by encryption, not by patents, but by a family oath and the silence of emperors.

The end.

Before you start

📚

Python Basics

Prerequisite coding course

Try It Yourself

Choose your level. Everyone starts with the story — the code gets deeper as you go.

Level 0: Listener

No coding needed — learn the science through the story

What You'll Discover

The chemistry of fire — exothermic reactions, the fire triangle, quicklime-water reactions, and why Greek Fire burned on water.

The big idea: "Greek Fire" teaches us about Combustion Chemistry & Thermodynamics — and you don't need to write a single line of code to understand it.

The Fire Triangle: What Fire Needs

Light a candle. What do you see? A flame, wax melting, a wick glowing. But what's actually happening is a chemical reaction — the wax (a hydrocarbon) is reacting with oxygen from the air to produce carbon dioxide, water vapour, and energy (heat and light).

Every fire needs three things — the fire triangle: fuel (something to burn — wax, wood, petrol), oxygen (from the air), and heat (enough to start the reaction). Remove any one, and the fire goes out. Blow out a candle? You cool the wick below ignition temperature (removing heat). Smother a fire with a blanket? You cut off oxygen. Run out of wood? No fuel.

Greek Fire was terrifying because none of these methods worked. Pouring water on it didn't cool it — the quicklime component reacted with water exothermically, adding heat. Smothering it didn't work because the sticky liquid spread across any surface. And removing fuel was impossible because it adhered to everything it touched.

Understanding why ordinary firefighting failed on Greek Fire requires understanding what each side of the fire triangle means at the chemical level — and how Greek Fire attacked all three defences simultaneously.

Check yourself: A grease fire in a kitchen should NEVER be put out with water. Why? (The water hits the hot oil, instantly vaporizes, and the expanding steam can spray burning oil everywhere. Same principle as Greek Fire — water makes some fires worse.)

Key idea: Fire requires three things: fuel, oxygen, and heat (the fire triangle). Removing any one extinguishes the fire. Greek Fire was devastating because its chemistry defeated all three standard extinguishing methods — water added heat, smothering failed because it spread, and removing fuel was impossible because it stuck to surfaces.

Exothermic Reactions: When Chemistry Produces Heat

Not all chemical reactions need heat from outside — some produce their own heat. These are called exothermic reactions (from Greek: exo = outside, thermos = heat — heat flowing outward from the reaction).

You experience exothermic reactions every day. Hand warmers contain iron powder and salt — when exposed to air, the iron oxidizes (rusts), releasing heat. The reaction is slow enough to warm your hands for hours without burning them.

But some exothermic reactions are violent. Quicklime (calcium oxide, CaO) reacts with water in a fiercely exothermic reaction: CaO + H₂O → Ca(OH)₂ + 65 kJ of heat per mole. That's enough heat to boil the water and raise the surrounding temperature above the ignition point of many fuels.

This is likely how Greek Fire worked on water. The quicklime component absorbed the water you poured on it, reacted exothermically, produced intense heat, and reignited the petroleum component. Pouring water on Greek Fire was literally feeding the reaction.

Try this (with adult supervision): Get a small piece of quicklime from a garden centre (it's sold for adjusting soil pH). Place it in a metal dish and add a few drops of water. It will fizz, steam, and get HOT — too hot to touch. This is the same chemistry that made Greek Fire impossible to extinguish with water.

Key idea: Exothermic reactions release heat as a product. Quicklime (CaO) reacting with water releases 65 kJ/mol — enough to boil water and reignite surrounding fuel. This is why water made Greek Fire burn harder: the water activated the quicklime, generating more heat instead of cooling the fire.

Sign up free to keep learning

Access all 130+ lessons, quizzes, interactive tools, and offline activities

or sign up with email

Oxidizers: Bringing Your Own Oxygen

Ordinary fire needs oxygen from the **air** — take away the air and the fire dies. This is why smothering works on most fires: cut off the air, cut of...

Story Progress

Ready to Start Coding?

Here is a taste of what Level 1 looks like for this lesson:

Level 1: Explorer — Python

import numpy as np
import matplotlib.pyplot as plt

# Your first data analysis with Python
data = [45, 52, 38, 67, 41, 55, 48]  # measurements
mean = np.mean(data)

plt.bar(range(len(data)), data)
plt.axhline(mean, color='red', linestyle='--', label=f'Mean: {mean:.1f}')
plt.xlabel("Sample")
plt.ylabel("Value")
plt.title("Combustion Chemistry & Thermodynamics — Sample Data")
plt.legend()
plt.show()

This is just the first of 6 coding exercises in Level 1. By Level 4, you will build: Build a Combustion Simulator.

Free

Level 0: Listener

Stories, science concepts, diagrams, quizzes. No coding.

You are here

Enrolled

Levels 1-4

Python, NumPy, Matplotlib, real projects, mentorship.

Stay Updated

Join Waitlist

Get notified when enrollment opens for your area.

Notify Me

Level 0 is always free. Coding levels (1-4) are part of our 12-Month Curriculum.

The Roman Aqueducts Egyptian Embalming

Level 0: Listener

No coding needed — learn the science through the story

What You'll Discover

The chemistry of fire — exothermic reactions, the fire triangle, quicklime-water reactions, and why Greek Fire burned on water.

The big idea: "Greek Fire" teaches us about Combustion Chemistry & Thermodynamics — and you don't need to write a single line of code to understand it.

The Fire Triangle: What Fire Needs

Exothermic Reactions: When Chemistry Produces Heat

Sign up free to keep learning

Access all 130+ lessons, quizzes, interactive tools, and offline activities

or sign up with email

Oxidizers: Bringing Your Own Oxygen

Ordinary fire needs oxygen from the **air** — take away the air and the fire dies. This is why smothering works on most fires: cut off the air, cut of...