C’mon. Obvious. If this was done in 499 B.C.
It’s no longer a secret.
Apparently Histiaeus had a hissy fit about his life with Darius as the Persians fought the Scythians and decided to chnage stuff up. Secretly.
Well. He got one of slaves. Had said slave’s head shaved and then tattooed with a secret message.
Waited for slave’s hair to grow back and then sent him off to Miletus…or someone else.
History is so twisted it could’ve been Kermit the frog.
P.S. I’ve known this STORY for decades. Fact!