Espionage is sometimes known as the world's second oldest profession (after prostitution, of course). An account of spies hiding on a prostitute's roof can be found in the Book of Joshua, and Sun Tzu's The Art of War, from 500 BCE, explored advanced methods of espionage at a time when there were only 100,000,000 people to spy on worldwide (for reference, about the population of Ethiopia in 2016). Famous and notable spies from history aren't limited to black-suited secret agents sprung from paranoia in the Cold War.
There were, in fact, sophisticated spies sneaking letters across enemy lines in the Roman Empire and cryptographic pioneers employing invisible ink during the Revolutionary War. The historical spies on this list run a wide gamut, from Ancient Chinese spies to English spies, American spies, and even spies in the Bible. Read on for fascinating espionage facts from throughout history.
According to Jeffrey Burd of Northeastern University, the oldest known reference to espionage is in the Old Testament. Rahab, a prostitute in Canaanite town Jericho, was forced to hide two Jewish spies on her roof, under bundles of flax. The spies, pictured flanking Rahab in the painting above, were on a mission for Israelite commander Joshua, who was following God’s orders to murder all Canaanites. Which sounds a bit extreme, but it is the Old Testament.
When Canaanite soldiers found out about the spies, Rahab refused to give them up. The spies agreed to spare her and her family’s life for her kindness: all she had to do was mark the window of her house with a red cord, signaling the troops to skip her house when it came time to cleanse the area. Some scholars think the red cord might have gone on to function as the red light does in Amsterdam, marking the location of a bordello (but others say “the parallel is almost too good to be true”).
Sun Tzu’s The Art of War (500 BCE) has a chapter called “Employing Spies,” which has been called “a seminal work in the world history of espionage.” In his treatsie, Sun Tzu argued foreknowledge is power: espionage can prevent “commotion at home and abroad” caused by warfare’s “heavy burdens on the people.” Sun Tzu dismissed traditional, superstitious methods of foreknowledge, emphasizing human intelligence. At the core of his principles of espionage was the concept of compartmentalization.
Compartmentalization is, arguably, why people love spy stories. It’s the engine driving the drama: Who knows what, and how? Compartmentalization ensures no single spy knows everything, meaning if they're captured, spies won’t know enough to compromise a mission. Sun Tzu advised military leaders to employ several different classes of spies, including now-classics such as double agents, moles, and keep them compartmentalized, a process he called the "divine manipulation of the threads.”
Roman spies used carrier pigeons as one of their many methods for disseminating intelligence and counter-intelligence. As Rose Mary Sheldon writes in Intelligence Activities in Ancient Rome: Trust in the Gods But Verify, military leader Hirtius trained pigeons to carry letters by starving them and keeping them in the dark near the city walls of Mutina, where fellow soldier Decimus Brutus was besieged.
The idea was to force the pigeons to crave food and light, so when they were released, they would carry letters, tied to their necks with human hair, to the highest nearby spot. Brutus, unable to leave the city but free to walk within it, would receive letters, placing food in the same spot to train the pigeons to seek that location as a trusted source of nourishment.
RM Sheldon writes in Espionage in the Ancient World that “no secret was better kept than the recipe for Greek Fire.” Greek Fire was essentially proto-napalm: a mysterious incendiary weapon that produced almost inextinguishable flames, even on the surface of water, making it a devastating naval weapon. The exact recipe and method Greek fire has been lost, but history tells us Byzantine armies, around 678 CE, managed to keep the secret from their enemies using counterintelligence methods, including compartmentalization. Military leaders spread the secret among an elite group of spies and produced the necessary components independently at remote sites.