The Republic

The Republic is a Socratic dialogue, authored by Plato around 375 BC, concerning justice, the order and character of the just city-state, and the just man. Written after the Peloponnesian War, The Republic reflected Plato's perception of politics as a dirty business that sought mainly to manipulate the unthinking masses. It failed to nurture wisdom.

It starts out as a dialogue between Socrates and several young men on the nature of justice. It's a classic for good reason, so if you're interested in ancient philosophy or politics at all, it's a must read.

The revolutionary thing about Socratic philosophy (and Plato picked up part of the lesson at least) is that it encouraged real dialogue. And we've been talking about it ever since.