Tattooed messages and wax tablets: steganography in Herodotus

Before enciphering a message one can try to hide it. This is the idea of steganography, covered writing, and its earliest testimonies are found in the Histories of Herodotus, written in the fifth century BC. The historian from Halicarnassus relates several episodes in which a decisive message crosses enemy lines not because it is unreadable but because no one suspects that it exists.

The slave's shaved head

The most famous story concerns Histiaeus, tyrant of Miletus, detained at the court of the Persian king Darius in Susa. Wishing to urge his son-in-law Aristagoras, who governed Miletus, to rebel against the Persians, Histiaeus had the head of his most trusted servant shaved, marked the message on his skin and waited for the hair to grow back. He then sent the servant to Miletus with the sole instruction to have his head shaved again in front of Aristagoras.

According to Herodotus the message, which called for revolt, arrived just when Aristagoras was already considering rebellion. It was one of the factors that led to the Ionian Revolt, which began around 499 BC, and thus, indirectly, to the Persian Wars. The method was slow, since it required weeks of waiting, but almost impossible for a guard along the road to detect.

Demaratus and the wax tablet

Another episode, in the seventh book, concerns Demaratus, a Spartan king in exile among the Persians. Having learned that Xerxes was preparing the expedition against Greece, he decided to warn Sparta. He took a folding tablet, scraped off the wax, wrote the message directly on the wood and then covered it with fresh wax. To the inspectors along the way, the tablet looked blank.

In Sparta no one understood what the object meant, until Gorgo, daughter of King Cleomenes and wife of Leonidas, suggested scraping off the wax. Beneath it the warning appeared. Herodotus himself is cautious about Demaratus's intentions, but reports the story as it had been handed down to him. Gorgo, thanks to her insight, has become a figure remembered in every history of secret writing.

Harpagus's hare and other devices

In the first book Herodotus tells how the Median noble Harpagus, determined to push Cyrus into revolt against King Astyages, hid a letter in the belly of a freshly killed hare and entrusted it to a servant disguised as a hunter. In an age of watched roads, the problem was not to make the text incomprehensible but to get it past the eyes of the guards unnoticed.

A century later Aeneas Tacticus devoted a chapter of his treatise on the defence of besieged cities to ways of sending secret messages: letters hidden among a messenger's personal belongings, or texts marked by tiny holes pricked above or below the letters of an ordinary book. This last device, in various forms, has been used down to modern times.

The term steganography would be coined only at the end of the fifteenth century by Trithemius, but the practice was as old as war and diplomacy. The episodes in Herodotus, whether exact chronicle or tales embellished by tradition, show that hiding a message has always been, at least as much as enciphering it, an art of cunning.