For many years Cassius Dio’s Romaika (c. AD 160 - c. AD 230) has served as a quarry for the reconstruction of lost sources and the historical narrative. The view of the Roman Republic held by this member of the imperial elite, however, has hardly been considered. This work combines two separate strands of research, in that it examines the criteria according to which he employed his sources: he adhered to an ideal of a harmonious society which was particularly influenced by the Stoic Poseidonios (c. 135 - c. 51 BC), according to which everybody served for the good of all.