The Secret History of the Mongols

The Secret History of the Mongols was a book obtained by Ezio Auditore da Firenze in the 16th century from one of Constantinople's many book shops.

Summary
''Written by an unknown author, or authors, "The Secret History of the Mongols" is the oldest recorded example of the Mongolian language. Though largely about the reign of Genghis Khan, the book was written some time after the famous conqueror's death.''

Reference

 * Assassin's Creed: Revelations