Historic messages and documents obscured by incomprehensible ciphers can be found in libraries and archives all over the world. Artificial intelligence is helping historians crack open these mysterious texts. Deep in the archives of the Vatican library, a mysterious hand-written book, scrawled with strange symbols, had lain unread for more than 400 years. Its cryptic pages apparently concealed secret remedies "for affections of the human body", according to some text scratched inside the cover.