Herculaneum, a town on the Bay of Naples that was buried beneath volcanic ash when Vesuvius erupted in AD 79, has only been partially excavated. Some buildings stand open to the sky; others, such as the theatre, can only be accessed through cramped and winding tunnels; many lie entirely entombed within rock. A visitor’s reaction to this can be an interesting gauge of character. The glass-half-full person will exult in the chance to walk the streets of an ancient city. The glass-half-empty person will wish there were more streets to walk. In Herculaneum, where furniture, bread and figs were all carbonised by the pyroclastic surge, the trace elements of life as it was lived in the heyday of the Roman Empire can serve to tantalise as well as satisfy the curious. To study the distant past is always to be greedy. It is to be like Orpheus, snatching after ghosts.

We can never know enough. This is not an exclusively modern feeling. Two thousand years ago, when Vesuvius erupted, a longing to make sense of what was happening lured antiquity’s most celebrated encyclopedist to his death. Pliny the Elder’s lifework, the Natural History, was a colossal monument to his insatiable inquisitiveness: thirty-seven volumes, crammed with facts strip-mined from some two thousand works, covering the entire breadth of available knowledge. Whether it was prescribing blood from a lamb’s testicles as a deodorant, discoursing on the intelligence of elephants, estimating the distance of the earth from the moon or identifying the only person to have laughed on the day he was born (Zoroaster), Pliny had pretty much everything covered. Inevitably, he made sure to describe the world’s volcanoes. Vesuvius, though, was not on his list. Pliny, like the inhabitants of Herculaneum, Pompeii and the various other towns planted on Vesuvius’s foothills, had no idea that it was a volcano. And so, when it erupted, the great encyclopedist inevitably wished to explore this remarkable occurrence close up, a commitment to field research that resulted in his asphyxiation by ash.

The details of his death were recorded years later by his nephew Pliny the Younger (as posterity remembers him). Seventeen at the time, he was busy with the Roman equivalent of his A levels and so turned down his uncle’s invitation to sail with him into the heart of the pumice storm. Lacking in heroism this decision may have been, but it was eminently sensible. Even in the naval base of Misenum, at a distance of some thirty kilometres from the volcano, Pliny the Younger was only just able to make an escape. Daisy Dunn, who opens her biography of him with a brilliantly vivid description of Vesuvius’s eruption, gives her account the appropriate shading of an apocalypse: ‘The cloud descended upon the earth and covered the sea until neither the island of Capri, nor even the promontory of Misenum itself, was visible on the horizon. Ash began to fall, only lightly, and hardly noticeable at all against the thick gloom that pressed them from behind, spreading over the earth like a torrent.’

Dunn’s book, then, begins with a bang. Fortunately for Pliny the Younger – if less so for Dunn herself – nothing else in his life ever rivalled the eruption of Vesuvius for sheer explosive impact. Over the course of a long and distinguished career, he practised as a lawyer, held a succession of important offices, hobnobbed with the Emperor Trajan and had a run-in with a group of Christians. His letters – of which 247 have survived – hold up an incomparable mirror to the governance of the Roman Empire at its height, and as such have always been treasured by historians of the Pax Romana. Peace, however, by its very nature, is less eventful than war. Dunn’s previous book, on Catullus, had as its backdrop the implosion of the Roman Republic, an incomparably dramatic episode, rich in extraordinary characters and convulsions. The age of Pliny the Younger offers fewer such excitements. Throughout his life Pliny himself remained recognisably the same person who, as a teenager, had opted to keep his nose in his books rather than head towards an erupting volcano.

In the hands of a lesser historian than Dunn, this might have made for a dull book. That In the Shadow of Vesuvius is never less than compelling is due principally to two things. The first is the subtlety of its structure. Rather than give us a strictly chronological biography, Dunn opts instead to trace the rhythms of her subject’s year. The section on Saturnalia – which Pliny, funster that he was, liked to spend in his study – comes with a ghost story set in Athens, the one on spring with a tour of his gardens, and that on summer with a visit to one of his farms. Episodes from his political career are seamlessly interwoven with more intimate details: the murderous Emperor Domitian buries a Vestal Virgin alive; Pliny’s wife – to Pliny’s own profound grief – suffers a miscarriage. Rather than provide us with merely a biography of a magistrate, Dunn gives us a portrait of an entire way of life.

A sophisticated structure is not the sole reason for this book’s success. Dunn also knows how to work a sentence. Without ever veering into historical fiction, she consistently succeeds in bringing what might otherwise seem dusty and remote to vivid life. Writing about the road that linked Pliny’s Tuscan estate to Rome, for instance, she describes how ‘the Via Flaminia had recently been relaid with black basalt from the volcanic provinces just north of the region, each luscious slab swollen and organic, like a loaf that had burned and spilled over its tin’. It is not just immediacy that Dunn gives us, however. If there is much about Pliny’s world that she makes seem familiar, then there is just as much that she makes seem very strange. Putting the book constantly in its shadow is the Natural History, that incomparable compendium of Roman knowledge. Be it menstruation or painting or oysters, we see the world of the nephew through the eyes of the uncle. In the Shadow of Vesuvius may be a biography of Pliny the Younger, but it would have been considerably less stimulating without the presence of Pliny the Elder.

The result is a portrait of the Roman Empire that gives the reader something of the shiver down the spine that Herculaneum can inspire: a sense that we are as close to the vanished world of two millennia ago as we are ever likely to get. Is it enough? That depends, of course, on whether you see the amphora as half empty or half full.