In book 36 of his Roman History Cassius Dio devotes about one third of the whole book, which covers the events of four years, to one particular event: the vote in 67 BC of the well-known lex Gabinia, which provided Pompey with an imperium extending over the whole Mediterranean sea and its coasts, in order to crush the overwhelming spread of piracy. This unusually extensive passage, which includes several speeches, betokens a conscious choice of Dio to shed light on one of the extraordinary commands of Pompey. The inquiry I propose tries to elucidate the meaning of that choice, by examining the relations between these long chapters about the lex Gabinia and other passages devoted to similar matters in different parts of the Roman History. By focusing on Dio’s view of some turning points in the last years of the Roman Republic, such a comparison will make manifest for us the particulars of his reflection about the passage from Republic to Empire. It should also exemplify the coherence of his thought throughout his work, in the wider perspective of his understanding of the politeiai of Rome.