This is a small series of texts about a big subject, and since a picture is proverbially worth a thousand words I want to begin it by talking about a very large picture that can help us to see what political philosophy is all about. The picture in question was painted between 1337 and 1339 by Ambrogio Lorenzetti, and it covers three walls of the Sala dei Nove in the Palazzo Pubblico of Siena.