Commentarii de Bello Gallico (The Gallic Wars)

Caesar's Commentaries, by Julius Gaius Caesar Teaches that while technology will change and political systems will be distinct and nuanced, the human animal is just about the same. When I see something that people did then that they still do today, I find that I can predict what a group of people is likely to do in a given situation in the future. This both blows my mind as things "click" and makes me sad. In either case, I'm better prepared.