For as long as there has been war, there has been a need to reveal the enemy’s ends, ways, and means. This was no less true in ancient Greece where generals and statesmen relied on espionage to reveal the intentions and capabilities of their adversaries.

The philosopher Plato believed that the ancient Greek states were in a constant state of war, whether declared or undeclared. It was within this grey zone that the subtleties of espionage took place, a dimension of foreign affairs that remains true to this day.

Like the practice of spying itself, the sources regarding espionage in ancient Greece are murky. Nevertheless, there is enough evidence to paint a compelling picture of covert intelligence gathering across the epochs of Greek antiquity.

Espionage in the Illiad and Odyssey

The historicity of Homer’s works on the Trojan War remains a point of debate, but the consensus among historians is that a conflict took place in the Bronze Age at the archaeological site today identified as ancient Troy.

Homer alluded to acts of espionage in both the Iliad and the Odyssey. The poet’s accounts are useful because they reveal acts of spying employed in ancient Greece, whether they reflect these practices at the somewhat uncertain period of Homer’s authorship or the more distant time of the Trojan War in the 12th century BC.

In the Iliad, Homer describes how Odysseus and Diomedes embark on a reconnaissance mission one night to find out more about the Trojan Army’s plans. That same night, a Trojan by the name of Dolon promises Hector that he will spy on the Greeks and infiltrate their camp. He sets out wearing a wolf pelt, a weasel skin hat, and a bow.

Unfortunately for Dolon, he is captured by Odysseus and Diomedes. The two Greek heroes promise to spare his life in return for intelligence on the Trojans, which Dolon gladly provides in the belief that he will escape the encounter unharmed. Odysseus and Diomedes uncover a great deal of useful intelligence, but renege on their deal and cut off Dolon’s head.

Homer also references espionage in the Odyssey. During one scene, Helen recounts how Odysseus infiltrated Troy dressed as a house slave. In this disguise, he was able to obtain useful intelligence for the invading Greeks.

Spying in Ancient Greece: From Athens to Macedon

In an academic paper published in the journal Greece & Rome, historian J. A. Richmond explains how spying was used in various scenarios in ancient Greece.

The ancient Greeks understood the importance of information in warfare. For example, in the middle of the fourth century BC, Aeneas Tacitus, a renowned Greek military writer, emphasized the significance of what we now recognize as Military Intelligence. He stressed the crucial role of possessing extensive knowledge about the geography of one’s own nation in effectively conducting defensive warfare.

According to Richmond, the ancient Greeks obtained intelligence through a variety of methods, although spying was conducted far more informally than it is today by national intelligence agencies.

Ports were an excellent place to obtain information and intelligence. Merchants were among the most well-traveled people in antiquity and brought news from distant locales. Foreign ambassadors could also be a valuable source.

There were also opportunities to sow misinformation. For instance, the ancient Greek concept of xenia (Greek: ξενία), or hospitality, could be taken advantage of. Foreign guests were generally expected to provide sound and honest foreign policy advice if questioned, but a less scrupulous guest might provide misleading information to confuse a potential adversary.

Those caught spying could expect severe punishment. Enemy spies in Athens were typically tortured and executed. One man, Anaxinus, who claimed that he was in Athens to buy products for the Macedonian queen was charged with espionage and put to death.

Spies might also conduct sabotage. Acting as an agent for King Philip II of Macedon, Antiphon, attempted to set fire to the Athenian arsenal at Piraeus. Antiphon was caught and put to death for attempted arson.

Espionage and Reconnaissance used by Alexander the Great

Alexander the Great likely inherited an understanding of espionage and covert means from his father Philip, who used agents and bribery to infiltrate and undermine Athens.

According to Plutarch, the young Alexander was keen to question Persian ambassadors visiting his father’s kingdom. From a young age, his mind was attuned to the dimensions of war, and he asked the ambassadors about the lengths of roads in Asia Minor and the skill of the Persian king as a commander.

As the historian D. Engles points out, the ancient sources on Alexander’s intelligence system are unfortunately fragmentary and unclear. It is difficult to determine what procedures Alexander’s spies, scouts, and agents used to uncover intelligence. When intelligence is mentioned in ancient Greek sources, little is said of the spies themselves, and the focus is instead given to Alexander’s use of that intelligence.

Nevertheless, Egnles maintains that Alexander sent forward diplomatic envoys to neighboring countries to obtain strategic-level intelligence before conducting a military campaign. He also interrogated high-ranking officials from these nations to obtain more information before launching an invasion.

In terms of tactical intelligence during a campaign, Alexander would have relied on a variety of sources, such as local guides and his own scouts. It was just as important to uncover the geography of the land for logistical purposes as it was to discover the composition of an enemy army before a battle. After all, Alexander’s difficult march across the Gedrosian Desert proved more deadly than many of his battles.