Starting with Malthus, several commentators have identified some quantitative elements in the work of Plato that led them to consider him a precursor of demographic thought. This article shows that this interpretation runs against the existence of contradictions between the text of Laws and Republic, and that a demographic point of view is not consistent with the profound coherence of Plato’s thought. A fascination for mathematics and the Pythagorean influence are part of the explanation. But above all, it is the concept of the City, at the same time an ideal utopian model and a concrete social construct, that provides the key to Plato’s “demographic” thought. Faced with the fundamental problem of power and justice, Plato proposes as a solution the restoration of harmony between the City as a political entity and the citizens who compose it. This philosophical approach is complemented by polemical hostility towards the democracy that was, according to him, responsible for the decadence of Athens. Philosophy and the political history of Greece in the fifth and fourth century B. C. are thus essential to an understanding of the meaning of measures that are wrongly qualified as demographic and eugenic and suspected of arising from a totalitarian vision when, in truth, they refer to a concept of man that is quite different from ours.