The Spartan scytale is a cylindrical staff around which a strip of leather or parchment was wound to write a message; unwound, the strip showed scrambled letters that could only be read by winding it around a cylinder of the same diameter. It is the first documented physical transposition-cipher device in the Western tradition. The sources are Plutarch (Parallel Lives, c.100 AD) and Thucydides (History of the Peloponnesian War, c.400 BC). There is academic debate over whether the scytale was actually a cryptographic system or a method of authenticating the messenger: historian David Kahn argues that its main function was to verify the bearer's identity, not to hide the content. The c.700 BC dating is conventional; the earliest explicit mentions are from the 5th century BC.