TIL in 499 century BC, king Histaiaeus (ancient Greece) sent secret military messages tattooed on bald heads of messengers. After the hair regrew, they sent the messengers. In the destination they were shaved again to reveal the message.

https://en.wikipedia.org/wiki/Histiaeus
#til #todayilearned
https://www.reddit.com/r/todayilearned/comments/1gje47i/til_in_499_century_bc_king_histaiaeus_ancient/