Death did not come quickly for everyone living in the shadow of Vesuvius on 24 August AD79. The busy city of Pompeii and upmarket resort of Herculaneum were smothered into immortality by a three-metre blanket of volcanic ash and pumice from the eruption. Many people were crushed or trapped in the dwellings and temples where they took refuge. The following morning, a cloud of hot gas and ash swept in to suffocate the survivors.
Many centuries later, the horrible reality was painstakingly unwrapped by archaeologists. The evidence has remained in Italy until this year. The British Museum's new show, Life and Death in Pompeii and Herculaneum, will tell the story graphically when it opens in London on Thursday. The exhibition is, to use a possibly unfortunate phrase, groundbreaking – revealing art and everyday life through exhibits that have previously never been allowed beyond the Bay of Naples.
The British Museum's curators persuaded the archaeological superintendent in Naples to allow the stories of these carbonised communities to be unlocked in London. As a result, the Italian city's Archaeological Museum is looking a little empty, and some pieces from the sites themselves are missing. Even so, for a properly rounded understanding of life and death in Pompeii and Herculaneum, you need to curl around the magnificent arc of the Bay of Naples and add essential extra dimensions. Starting with Vesuvius herself.
Knowing what we do now about the nature of tectonic plates and, in particular, the brittle crust of earth in southern Italy, it is a tribute to faith (or fatalism) that anyone lives in the skirts of a hyperactive volcano such as Vesuvius. In fact, three million people cram into the ribbon of shoreline between the Mediterranean and the unstable mountains. Almost all of them glimpse their nemesis many times each day. From the harbour at Naples around to the beach at Sorrento, Vesuvius creeps into every field of vision. At a distance, her shape is softened by the haze to resemble, say, a gentle swell on the sea. The closer you get, the more you notice the imperfections. By the time you start the journey to the crater, the scars have become deep wounds.
As the minibus from Torre Annuziata railway station breaks free of the tree line, the cargo of excited tourists comes face to face with the restless planet in all her menacing nakedness. The terrain has the colour and consistency of a well-baked crumble just emerged from the oven.
Once you have paid €11 to pay your respects to Mother Earth, and zigzagged up the cinder path to the rim of the crater, you are likely to be cheerfully breathless. On a sunny spring day, the enterprising vendors of volcanic souvenirs are also in a good mood. But Vesuvius is seething. While the crater looks as though someone has carelessly scooped it out with a trowel, the fumes that belch from fissures far below tell the real story: Eurasia collides with Africa here, creating a landscape as crumpled as Frankie Howerd's face. And Vesuvius is the pressure valve.
That summer morning in AD79, the Roman gentry were relaxing at their seaside residences in Herculaneum when the world exploded. The images of life at the moment of death are sharply preserved. Walk down from the railway station at Ercolano Scavi and in 10 minutes you slip back a couple of millennia. While today's residents hang out the washing, you can wander through the lives of their ancestors. Surplus wealth was expended in the time-honoured fashion of creating glamorous villas, with mosaics on the floor, walls decorated with frescos, ceilings supported by stout columns.
Everywhere at Herculaneum there is a sense of playfulness: hunting scenes picked out in dazzling colour, amphora lined up for the summer's wine that never came. Human forms have survived only in the elegant shape of extravagant sculptures. Their lips may be sealed, but your jaw will drop as you wonder at the fragment of ancient Rome sealed for centuries.
You may also be amazed at how 21st-century suburbia crowds around the site – and how Unesco still awarded World Heritage status to a collection of sites in a scrum of modernity. Elsewhere on the globe, the body demands the removal of telegraph poles before a location makes the list. I guess the officials settled for preserving the status quo that is so spectacularly preserved at Herculaneum.
Vesuvius is not the only Italian volcano with its own railway – Etna, on Sicily, has the Circumetnea. But the Circumvesuviana, completed in 1932, connects more wonders than any other line. A couple of stops down the line takes you to Pompei Scavi, where the A3 autostrada meets the SS18 highway and the 1st century AD.
Should you have time to visit only one Vesuvian victim, make it Pompeii. Most of the 16,000 lives were lost here in AD79, as a prosperous trading port became a fossil almost instantly. Two millennia on, you can explore Pompeii as you might a novel Italian town. Even the modern pizzeria in the middle does not destroy the ancient illusion.
The city that rambles across the volcanic foothills is astonishing. In parts it looks not so much half-destroyed as half-built – as indeed it was, because repair work after a massive earthquake in AD62 was still going on at the time of the eruption. Athletic, be-toga'd statues contrast with the pitiful sight of a writhing human figure. His tortured shape is preserved in plaster, encased in glass, on which tourists train their smart phones. The same devices can monitor global seismic activity at earthquake-report.com. Progress, indeed.
You need no technological toys to visualise life in Pompeii, and realise how constant is humanity's quest for bread and circuses – essentials plus entertainment – and spiritual enrichment. Between the bakeries, baths and dwellings and temples, follow the chariot tracks. The grooves carved in the cobbles lead the eye through the city streets and beyond into the verdant hinterland colonised by vines and olive trees. Not even the British Museum can transplant the setting from 40 degrees north to London WC1B 3DG.
Next stop on your personal progress is the singular treat most overlooked by visitors. The Roman villa of Oplontis sits neglected just down from Torre Annuziata railway station. Yet in terms of elegance it is the outstanding survivor of Vesuvius, with far more panache than Pompeii or Herculaneum. Want to waft through a Roman palace, feeling the weight of the mighty doors and being intimidated by sheer opulence? Well, you can and you should. The greatest contemporary artists of the Western world were engaged to create works of dazzling vivacity and delicacy.
Study the pictures of Roman rural bliss to discover surreal – even sinister – overtones, such as an apparently dismembered human head staring out from a colonnade, wide-eyed, at a peacock. Then wonder at your good fortune at gazing into the past in solitude while the crowds compete at Pompeii. A perfect place to finish – unless you prefer to indulge like a rich Roman. In which case: back to the Circumvesuviana with you. Board a train to the end of the line, and pay attention as the railway leaps across the deep gashes in the corniche. At Seiano, pop out for a moment on to the world's most vertiginous railway platform, suspended high above a gorge. It looks as if the post-war engineers patching Europe back together chose to run a viaduct straight across a geological fault line. Which, in a sense, they did.
Ten minutes later, you emerge at Sorrento, the punctuation for the line and the entire Bay of Naples. The Grand Hotel Excelsior Vittoria here claims to be the site of the villa of the Emperor Augustus, and boasts Roman remains in the gardens. When it re-opens for the summer next Friday, it will tempt visitors, and possibly fate, with a "Discover Pompeii Package" that includes a private tour of the ruined city. The Excelsior jostles with other 19th-century luxury hotels for the best cliff-top views so that guests can sip prosecco as their eyes rest over the Mediterranean and towards that violent volcano.
As you finish the glass, pause to reflect on this: amid all the scenes of art, nature and daily life depicted from that fateful summer of '79, I could find not a single image of the most visible element in their lives, and deaths: Vesuvius.
The main gateway to the Bay of Naples is Gatwick. Simon Calder paid £140 outbound on BA (0844 493 0787; ba.com) and €175 inbound on easyJet (0871 244 2366; easyjet.com); the latter also flies from Stansted, Liverpool and (starting 17 April) Edinburgh.
The Circumvesuviana train is the main artery around the Bay of Naples, connecting Naples (Porta Nolana and Centrale stations) with Sorrento. The English-language website, vesuviana.it/web/en, gives fares and times.
In Naples, Simon Calder stayed in the B&B del Corso at Corso Garibaldi 340 (00 39 081 204 087; bnbnapoli.it); B&B doubles from €49. In Sorrento, he stayed at the Hotel Linda at Via degli Aranci 125 (00 39 081 878 2916; hotellinda.it); B&B doubles from €70. A double with breakfast at Sorrento's Grand Hotel Excelsior Vittoria (00 39 081 807 1044; exvitt.it) costs €368. Its three-night Pompeii package (£849 per person in April) includes flights from Gatwick and a guided half-day tour of Pompeii through Classic Collection (0800 294 9324; classic-collection.co.uk).
Life and death in Pompeii and Herculaneum runs 28 March-29 Sept at the British Museum in London (020-7323 8181; britishmuseum.org/Pompeii; £15). Advance booking is recommended.