Some of us have been waiting years for this book. I was allowed to read a small section quite a long time ago, lest I commit unseemly errors in my fictional biography of Antonia Caenis, Vespasian's ladylove. Barbara Levick does not despise popular fiction; she is as rooted in real life as her down-to-earth subject must have been. Indeed, it is only because I know her to be an extremely jolly woman, and a fan of crime fiction, that I dare to comment on a work of such immense erudition in a discipline that is not mine.

That there was no major modern biography of Vespasian had been a howling omission, and luckily the need to evaluate the Flavian dynasty as a whole allows Titus and Domitian to be hauled in alongside their father. (Three for the price of one: how Vespasian would have loved it!) We may never know much more about any of them personally than can be cautiously extracted from their near contemporaries: Suetonius in particular, bursting with a tabloid desire to sneer at these middle-class upstarts - yet not quite daring to rubbish their political achievements in case he then looks incompetent. Even Josephus, their tame hack, has more to say to re-enactment groups about the Roman army's methods and kit than he can tell any of us about the men who led it. As biographers, these chaps are, I fear, strangers to the Eng Lit concept of a 'well-rounded character', posing problems which have to be skated round deftly by both Barbara and me in our different spheres.

Her method here, firstly, is to write history for grown-ups, not for wimps who need the story explained. Sticking with the Eng Lit analogy, you are expected to have read the book under discussion and be ready to do some critical analysis. Once you wake up and pay attention, of course, this is fine. The no-nonsense, 'let's get down to it' approach admirably suits her subject. Briefings in a Flavian camp or court must have been just as polite, yet just as brisk and factual. And there really is a story too, one which she enjoys telling. She takes flight in fine fashion when relating the great Judaean campaign and its inextricably interlinked manoeuvres to make Vespasian Emperor. As political and military history, this matches anything in Caesar, and is all the better for having at its centre a man you can warm to.

The man is vital. We see, moreover, that Vespasian was the proverbial right man at the right time. Acquiring the Empire at sixty, he had maturity and experience - plus convenient heirs. While definitely not a man 'with nothing to prove' (he was given an unexpected chance and certainly meant to make the best of it), yet in some ways he could relax; he lacked the dreadful po-faced striving for effect that characterised earlier emperors and even damaged his own sons. Taking over Rome when things could hardly have been worse, his task was enormous. As she examines the geographical and institutional fabric of that empire, Barbara Levick shows how he rebuilt each element intelligently and systematically, aided by the careful deployment of trusted personnel.

This is where she triumphs. I was struck by the enormous range of people, previously mere names in arcane textbooks, who are for the first time illuminated by swift character sketches, then given their precise relevance to events, their marriage ties mentioned, their personal aspirations subtly judged. For me, the book's finest achievement is this portrait of the whole Flavian period. Society in the AD70's and 80's comes alive in a way that normally only happened with the devious personalities on the long road to Actium and those hackneyed Julio-Claudians. How refreshing to explore a new cast. (Even better that so many of them seem to be honest 'doers' and 'fixers'.) The detail is stupendous. This is true scholarship. And it has a particular point: Levick persuades us that Vespasian had a genuine wish to do right. He was rebuilding the Empire not for a private challenge, like a hobbyist perfecting a matchstick model, but really to create a decent, rewarding environment for the people who lived there.

Ultimately she sets his achievement in context, judged as it now surely ought to be as the foundation for the Second Century heyday that has always seemed more glamorous - for reasons I could never understand, because what could be more interesting and exciting than to change chaos and bankruptcy into a system that runs well, where most people are content? And come to that, why should the Decline and Fall of an Empire fascinate so much more than its establishment and rise? We live in a corrupt and jaded society. It is encouraging to remember that after great cycles of ruin there may come renewal.

I am a closet administrator so I was bound to love this book. Just why did that famous Vespasianic charge on urine attract such attention? It was a tax-efficient, environmentally useful, brilliantly simple, humorous fiscal measure. Anyone who has been any kind of administrator has to marvel. Anyone who could invent it, has to be appealing.

So the subject matter attracts in itself: the portrait of an era, the tale-telling of events, the triumph of the man. There is another aspect. Barbara Levick's 'Vespasian' represents her own lifetime achievement as a historian and a teacher. For me it exemplifies what scholarship should be: the meticulous search for information not just because it is proper, but because it is also fun; the intelligent and practical judgement; the continuing evaluation of material; the desire to communicate; the sudden flash of wit that thrills. All of those are here. Any student of the period will need this book - and what's more, it will have its place in the creation of crime fiction too.

Lindsey Davis 1999