The article analyses Cassius Dio’s work and defines some social and cultural factors, mental attitudes, personal motives and career vicissitudes that formed and guided his political and historical views. Dio’s «Roman History» took its definitive conceptual shape in the late 220s. The main feature of that work is the expression of personal experience via historical narrative, his self-positioning as a senator-historian, who is the only one able to be a real «mediator» between Rome’s great past and his own days. The Roman past was important and significant for Dio so far as it remained in present and could be correlated with contemporary political processes. By using the means of precedent historiographic tradition, first of all that of Thucydides, he gives an account of the Roman history as a whole, paying special attention to the Late Republican and Augustan times and looking intently into the actual problems of the Severan age. The feeling of total crisis of the Empire led Dio to detecting system and institutional changes underlying historical developments of the past and present times and to work out a coherent program of state reconstruction and reforms. This program is most explicitly formulated in the famous debate between Agrippa and Maecenas in Book 52. These two speeches form a compositional and conceptual unity, but it is in the Maecenas’ speech that Dio suggests his responses to political challenges of his age. Some contradictions of the proposed program are more understandable if considered in the context of Alexander’s rule. Therefore, the final composition of Book 52 may be dated to the very end of the 220s, when Dio achieved the top of his career, was favoured by Severus Alexander and, having some influence upon the emperor, could aspirate at least partial realisation of his reformist thoughts. The complex of ideas and practical proposals expressed (though not in a straightforward way) in the Agrippa–Maecenas’ debate is on the whole the sum of Dio’s own political experience and reflections. As a political realist he excellently understood how changeable the good-will of a monarch could be and relied not on the ruler’s benevolence, but on the reorganisation of the governmental system. As a historian, Dio extends the repertoire of historiographic techniques at the expense of critical treatment of contemporary politics and direct appeal to political theory. All these features as well as the impressive amount of the narrative enable us to characterise Dio’s «Roman History» as a unique historical writing for the early 3rd century A.D.