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"(...) the Chinese would often write on exceedingly thin silk or paper, which they rolled into a ball and covered with wax. The messenger hid the ball, or "la wan," somewhere about his person, or in his rectum, or he sometimes swallowed it."

Ancient China
Cite from the book "The Codebreakers" by David Kahn.

"Demaratus, the son of Ariston, who was an exile in Persia, (...) as soon as news reached him at Susa that Xerxes had decided uponthe invasion of Greece, he felt that he must pass on the information to Sparta. As the danger of discovery was great, there was only one way in which he could contrive to get the message through: this was by scraping the wax off a pair of wooden folding tablets, writing on the wood underneath what Xerxes intended to do, and then covering the message over with wax again. In this way the tablets, being apparently blank, would cause no trouble with the guards along the road."

Histories, Herodotus (430 B.C.)
Cite from the book "The Codebreakers" by David Kahn.

"Histiaeus, wanting to send word from the Persian court to his son-in-law, the tyrant Aristagoras at Miletus, shaved the head of a trusted slave, tattooed the secret message thereon, waited for a new head of hair to grow, then sent him off to his son-in-law with the instruction to shave the slave's head. When Aristagoras had done so, he read on the slave's scalp the message that urged him to revolt agains Persia."

Histories, Herodotus (430 B.C.)
Cite from the book "The Codebreakers" by David Kahn.

"[...] I have uncovered certain ways, both numerous and varied, that are not to be entirely spurned whereby I can intimate my most secret thoughts to another who knows this art, however far away I wish, securely and free from the deceit, suspicion, or detection by anyone, using writing or openly through messengers."

Steganographia, Johanes Trithemius (1462 - 1516)

"The Cardano grille consists of a sheet of stiff material, such a cardboard, patchment, or metal, into which rectangular holes, the height of a line of writing and of varying lengths, are cut at irregular intervals. The encipherer lays this mask over a sheet of writing paper and writes the secret message through the perforations, some of which will take a whole word, others a single letter, others a syllable. He the removes the grille and fills in the remaining spaces with an innocuous-sounding cover message. (...) The dechipherer simply places his grille on the message he receives and reads the hidden text through the "windows". "

Girolamo Cardano (1501 - 1576)
Cite from the book "The Codebreakers" by David Kahn.

"Two accomplices in a crime have been arrested and are about to be locked in widely separated cells. Their only means of communication after they are locked up will be by way of messages conveyed for them by trustees -- who are known to be agents of the warden. (...). The prisoners, (...) are willing to accept these conditions (...) to be able to communicate at all, since they need to coordinate their plans. To do this they will have to deceive the warden by finding a way of communicating secretly (...)"

The Prisoners' Problem and the Subliminal Channel by Gustavus J. Simmons (1983)