Ancient tomes scribbled with incomprehensible text, thought to hold thought-provoking insider looks into mysticism and history—or a really awesome secret code.
So, 1499 isn't so much "ancient" history, but that's when an interesting German abbot, Johannes Trithemius, wrote a book on magic, or so they thought. Turns out it was one of the first books on cryptography, the art of secret messages and passwords!
Encryption is all the rage nowadays with computer hackers constantly getting at personal data. Turns out abbots in the 15th century had things to hide too, so they did it in deceiving text. What many thought was a book on magic and using spirits to communicate over long distances, "Steganographia" was actually an early work on cryptography and steganography.
The book was written in three volumes with the first two clearly being on the secret subject after the decryption key was published 100 years later in 1606. Until recently, it was thought that the third volume really was about magic, but the "magic formula" was cracked and shows more cryptology content.