First use of steganography

Dating back to the 5th century BC, steganography is one of the oldest methods of concealing secret information. According to the classical author Herodotus, it was first used by the tyrant Histiaeus, who shaved the head of a servant before tattooing a message on the poor man’s scalp. When the hair had grown back, the servant was sent to deliver his message - a warning of impending attack by the presumably slow-moving Persian army - which was revealed when the servant’s head was once more shaved. Histiaeus was the tyrant of the ancient Greek city of Miletus (modern-day Anatolia, Turkey).