The 5th century BC Greek historian, Herodotus, records how Histiaeus of Miletus, who was being held against his will by King Darius of Susa, sent a tattooed secret message to his son-in-law, Aristagoras. Histiaeus shaved the hair of his slave and tattooed the message on to the man's head. The slave was told that the procedure would cure his failing eyesight. When the slave's hair had grown back sufficiently to hide the tattoo, he was sent to Aristagoras, who shaved his head and read the hidden message. The message instructed Aristagoras to begin a rebellion.