Plato’s best-known work, The Republic was written around 380 BC. Largely a Socratic dialogue concerning justice, the order and character of the just city-state and the just man, it serves as the forerunner for such other classics of political thought as Cicero’s De Republica, St. Augustine’s City of God, and Thomas More’s Utopia. Among the ideas put forth are the eternal conflict between the world of the senses (the cave) and the world of ideas (the world outside the cave), and the philosopher’s role as mediator between the two. Also: Kallipolis, a hypothetical city-state ruled by a philosopher king, and the theory of forms, the immortality of the soul, and the role of the philosopher and poetry in society.