THE ROMANS HAD a word for moments in which the course of history was changed, when the gain of riches and renown or the loss of lives and liberty rested on a single decision - 'discrimen'. Tulius Caesar's crossing of the Rubicon might be held up as an exemplary instance of this: forbidden by his former ally, now his arch-opponent, Pompey, to re-enter Italy without first disbanding his battle-hardened legions, and facing prosecution in Rome for crimes perpetrated whilst he was consul in that city, Caesar chose to lead his army across the river, so topographically insignificant that its location would eventually be forgotten, and begin a civil war that would ultimately bring down the Republic. However, Tom Holland doesn't believe in discrimen, and neither, it seems, did Caesar. As he ordered his men into Italy he surrendered responsibility for his actions, famously declaring, 'Alea iacta est.' The invasion was the result of trespasses committed, intrigues incited and ambitions indulged long before. When Caesar used the phrase he was not being fatalistic, but rather recalling the gambling expertise of his youth, when as a fast-living urban fashionista he had time and again risked everything he had against his future glory, both financially and politically (the two were inseparable in the Republic). Caesar, as he proved by venturing into the Senate on the Ides of March, defied augury. What he paid attention to were the power-struggles and underlying inclinations of Rome and the Roman people, and it is to these that Holland's entertaining and ambitious narrative history - ranging over almost five hundred years, from the dethroning of King Tarquin to the unchallenged dictatorship of Augustus Caesar - looks for the reasons behind the Republic's undoing.

The chief characteristic of the Republic - and of the people, politicians and soldiers who belonged to and defended her - was tenacity. Everywhere in her daily life there was struggle: 'The difference between a senator campaigning for the consulship and a gladiator fighting for his life was only one of degree,'