  Yet even as Plato and Aristotle were writing, other Greeks were issuing cosmopolitan challenges. Perhaps the most obvious challenges came from the traveling intellectuals who insisted on the contrast between the conventional ties of politics and the natural ties of humanity. Notice, for example, the way Plato has the Sophist Hippias address the motley crew of Athenians and foreigners present at Callias’ house in Plato’s Protagoras (337c7–d3):