Marcus Tullius Cicero was the ancient master of the ‘save’ key. He composed more letters, speeches and philosophy books than most writers of any epoch; but more important than any particular work was that so much survived to define his time. He had a secretary, Tiro, who can reasonably be given the credit for researching, correcting, copying and casting out his master’s words. In Robert Harris’s three novels of Cicero’s life, Marcus Tullius Tiro, the freed slave who took his name as well as dictation from his boss, gets his full reward. Over more than 1,000 pages, the secretary is the narrator of how the world’s first great republic slipped into empire, a story that, thanks to the luck of literary survival, centres on Cicero as so many histories have before.

Dictator draws on the final 14 years of Cicero’s writings, beginning in the year 58 bc when, still famed and shamed for killing the Catilinarian conspirators in his consulship five years before, he chooses exile rather than an open fight with bigger, fiercer and suddenly united beasts, the plutocrat Marcus Crassus, the butcher-turned-constitutionalist Gnaius Pompeius and the genius of war and prose, Julius Caesar. How honest is Cicero — in public and in private — about why he is going? Compromise clashes with principle, events with expectations, until a triumphant return, and one by one the murders of all those beasts and his own murder.

Harris writes in his author’s note that these years are ‘arguably the most tumultuous era in human history’ before the rise and fall of Hitler. Most tumultuous? That is too great a claim. The years most significant for our understanding of what makes political history? Absolutely. Generations of writers have agreed that in some peculiar way, a very Ciceronian way in truth, the Roman age had room for the iconic clash of characters that later ages lacked.

Roman history was the past that most European politicians once knew. For a less knowing age Harris is not only a hugely successful writer of popular novels but a powerful writer about political practice. He starkly displays Cicero’s view of how the Roman Republic tottered from three-man to two-man to one-man rule, the stands of principle and struggles of compromise.

Tiro is the ubiquitous observer, his slim frame squeezed into the most privileged places. He sees his master at his best and worst. He gives vivid verdicts on Cicero’s unhappy wives. He sees Caesar’s assassination. He is on hand whenever news comes of battles won or lost. He is only occasionally unreliable about a fact. Something of a philosopher himself, he is an awestruck watcher of the stars.

Harris has a delightful mastery of the political then-as-now, the self-righteous war-criminal (Caesar with a hint of Blair), the mad, veteran autocrat (Caesar with a hint of Thatcher), the ‘eating-house plot’ (remember Granita and Gordon Brown), the ‘genius of mediocrity’, the abuse of writers by their families (where is the money in books?), and the last words in this noble trilogy, that ‘all that will remain of us is what is written down’.