The Book is therefore tailored to this choice audience. It cannot be exactly dated, but it seems reasonable to suppose, from tone and content, that it was written (in fact, dictated to slaves or perhaps freedmen) around 7 or 6 BC: Gaius, the elder of the boys by three years, would have been thirteen in that earlier year. It does however include a few pages – those dealing with his reception of the news of the murder of Julius Caesar – which appear to have been written at an earlier date. It is known too – and he confirms this in the text – that Augustus composed a fragment of autobiography while campaigning in Spain in 24 BC, and parts of this earlier book seem to have been incorporated in the text of the later memoirs written for his grandsons. Certainly there are passages where he seems less conscious that they constitute his audience. It seems unlikely too that either part of his Memoirs was fully revised by Augustus himself. The form in which we possess them doubtless owes something to his secretaries or literary executors.

Book I begins with Caesar's murder and ends with the deaths of Antony and Cleopatra fourteen years later. It tells the story therefore of the rise of the boy Gaius Octavius Thurinus (as he was still called in 44) to the position of supreme authority in the Roman world. It is a story of glittering achievement. Even two millennia later it remains astonishing, for at the time of his uncle's murder he was only nineteen, Rome was torn by faction and civil war, and no one could predict, none indeed predicted, that this slim youth could imprint his personality on the Republic, and succeed where Caesar, Pompey, Sulla and Marius had failed in restoring peace and order to a distracted world. That he did so is still remarkable, and his own account is gripping and, within the limits of political language, surprisingly honest: he does not shrink from confessing the cruelties and deceits unavoidable in his rise to power: in particular, his accounts of the Proscriptions of 43 and of the manner in which he wrested Antony's Will from the safe-keeping of the Vestal Virgins in order to publish it to his own political advantage are amazingly candid.