Stonehenge, with the possible exception of Big Ben, is Britain’s most recognisable monument. As a symbol of the nation’s antiquity, it is our Parthenon, our pyramids – although, admittedly, less impressive. Neil MacGregor, the former director of the British Museum, recalls that when he took a group of Egyptian archaeologists to see it, they were baffled by our national devotion to the stones, which, compared to the refined surfaces of the pyramids, seemed to them like something hastily thrown up over a weekend.

Unlike those other monuments, though, Stonehenge is more or less a complete mystery. Nobody knows for sure why, or by whom, this vast arrangement of boulders was erected on Wiltshire’s downlands, in the south of England, about 5,000 years ago. Into this void have rushed myriad theories, from the academically sober to the blatantly fantastic. Over the centuries, its construction has been confidently credited to giants, wizards, Phoenicians, Mycenaeans, Romans, Saxons, Danes and aliens. (According to one medieval theory, Merlin had it transported from Ireland to serve as the funeral monument for Britons slaughtered by Hengist, the treacherous Saxon.)

Since Stonehenge slipped into the written record in the medieval era, it has been a place to project our ideas of ourselves. It was said, by the 20th-century archaeologist and writer Jacquetta Hawkes, that “every age has the Stonehenge it deserves”.

And so today’s Stonehenge is not William Blake’s terrifying “building of eternal death”; nor is it Thomas Hardy’s “monstrous place”, where Tess of the D’Urbervilles sleeps her last night before being taken to be hanged. Nor is it even the Stonehenge of the counterculture, where peace-freaks revelled until they were brutally routed in “the Battle of the Beanfield” in 1985, one of the most notorious episodes in the history of British policing.

Our Stonehenge has none of this grandeur or pathos. Instead, it is at the centre of a peculiarly modern British circus – one that involves an agonisingly long planning dispute, allegations of government incompetence, two deeply entrenched opposing sides, and a preoccupation with traffic and tourism. This absurdist drama, entirely worthy of our times, is a long and bitter battle over whether to sink the highway that runs beside it into a tunnel.

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The A303, the road in question, is celebrated for the wonderful views it offers of the Stonehenge monoliths. But as one of the two major routes connecting the domesticated landscapes of the south-east of England with the wilder West Country, it is just as famous for its dire traffic jams, which begin as the highway narrows to a single lane near Stonehenge.

What could be a 10-minute ride through the 6,500-acre Unesco world heritage site in which Stonehenge sits is at peak times an hour-long, bad-tempered grind – a torture to holidaymakers making for Devon and Cornwall, a drag on the economy of the south-west of England and a bane to locals. According to David Bullock, who works for the national road-building agency, Highways England: “On Fridays, for a person living in Amesbury, it is quite a torrid affair, if you want to go anywhere.”

But this gridlock is not easily resolved. Diverting the road is hard to do: north of the current route lies Britain’s biggest Ministry of Defence training area, south of it pristine countryside. Simply widening it is unthinkable: the Stonehenge heritage site is a precious prehistoric landscape. Governments have been trying, and failing, to solve the problem of the A303 since the 1980s: numerous plans have been suggested and then dropped, at the cost of untold millions. A dizzying number of bodies have been involved, representing every possible interest-group and opinion, from roadbuilders, heritage organisations, government departments and councils to the Campaign for the Preservation of the Lower Till Valley, the Stonehenge Traffic Action Group, the British Horse Society and the organisation that protects Europe’s heaviest flying birds, the Great Bustard Group.

The current proposal, to widen and sink the road into a tunnel running for almost two miles, mostly about 600 metres south of the stones, was announced in 2014, although the basic idea goes right back to the 1990s. The main difficulty is the cost: the government has allocated £1.7bn, which is not enough for a passage sufficiently long to avoid the world heritage site. That means tunnel portals would be bored, and dual carriageways built, through an ancient landscape unique in the world. This protected area is home to traces of a mesolithic settlement long predating Stonehenge, the ancient “Avenue” linking the monument and the river Avon, and hundreds of bronze-age burial mounds, or barrows.

But the long planning process is entering its endgame. Later this year, a panel of inspectors will meet in Wiltshire and, over a period of six months, examine the evidence for and against the scheme. They will have three months to make their recommendation to the transport secretary, Chris Grayling. He will have a further three months to decide whether or not to accept it. Construction could start in 2021.

Tempting as it is to suggest that the dispute pits the forces of modernity against the defenders of tradition, the argument boils down to whether you think a major construction project in a world heritage site is absolute madness, or the commonsense solution to a long-term traffic problem. English Heritage, the national body that cares for Stonehenge, insists that doing nothing is not an option. It argues that the A303 will only get busier as new homes are built in the south-west – and that the tunnel, in any case, would significantly improve the “visitor experience” by returning the circle to its intended setting, without the intrusion of the sights and sounds of the A303. They also say that the plans have been carefully drawn up to avoid damage to prehistoric features, and that they are still working hard with Highways England to minimise their impact.

Battling English Heritage’s smooth assurances, however, is the Stonehenge Alliance – a coalition of NGOs, including Friends of the Earth and the Council for the Protection of Rural England. Supported by an eclectic band of well-wishers, including archaeologists, historians, farmers and druids, they think it is ridiculous to remove the sight of the stones from passing motorists. More seriously, they argue that the tunnel would “scar the Stonehenge landscape for ever”. Prof Mike Parker Pearson, the archaeologist who has done the most influential recent work on the monument, has entered the fray on the side of the Stonghenge Alliance. He calls the scheme “an unattractive British compromise: a bit of a tunnel, but one that is not long enough to protect the archaeology of the world heritage site”. In his view, the plan would amount to the biggest intervention in the landscape for 5,000 years – and all for a construction project that might have a lifetime of a century.

Stonehenge is both smaller and larger than you expect. From the middle distance it can seem surprisingly tiny, like seeing a celebrity in real life. Most tourists don’t ever get right up to the stones, since they are cordoned off. But if you are lucky enough to get among them (by booking special access, or by attending ceremonies held at the solstices and equinoxes) the monoliths loom massively, and seem full of threatening, or beguiling, character: dour and grey on a dull day, but an almost apricot pink when lit by a summer’s sunset.

Touching them is forbidden, although this has not always been the case: their surfaces are scarred with graffiti both ancient and modern, from images of daggers gouged out in the Bronze Age to Christopher Wren’s neatly carved signature. “You’d have thought he’d have known better,” said English Heritage archaeologist Heather Sebire disapprovingly, when we walked among the stones one dusk. Sebire is pro-tunnel: “Everyone knows the scheme’s not perfect. But it is the best we’re going to get at this point in time.”

There are some 1,300 stone circles in the UK, from the Ring of Brodgar in the Orkneys to the Merry Maidens in Cornwall, according to archaeologist Mike Pitts (pro-tunnel). But none of them is quite like Stonehenge. Two things make it unique, archaeologist Julian Richards (anti-tunnel) told me.

First are its lintels – the horizontal stones atop the great upright boulders. This act of placing stone on stone is what makes it Britain’s “first essay … in architecture”, as Samuel Johnson put it. (Its circular form inspired John Wood’s mid-18th-century Circus in Bath, itself the model for Oxford Circus and Piccadilly Circus, meaning, according to historian Rosemary Hill, it is the probably the ultimate ancestor of the British roundabout.) The second thing is that Stonehenge is the only neolithic monument in the UK to use stones not found locally. Only the taller “sarsens” are from Wiltshire. The smaller “bluestones” were quarried around 124 miles away in the Preseli Hills in Wales – an act of transportation that has long puzzled scholars.

To celebrate the millennium, an ill-fated project, funded with £100,000 from the national lottery, attempted to re-enact the fetching of a single three-tonne dolerite bluestone from Wales to Wiltshire. The original plan was for volunteers, some 40 a day, to wear “‘appropriate clothing’ of skins and furs”. But that had to be abandoned for safety reasons, according to Mike Pitts’ book Hengeworld – and many of the volunteers drifted away, disenchanted by the awful task. After eventually loading the boulder on to a boat at Milford Haven, from where it was meant to travel up the Bristol channel, a frisky wind saw it tumble into the sea. At this point it was rescued, using the un-neolithic technology of a crane, and transported on a flatbed truck to the botanical gardens in Carmarthenshire, 140 miles from Stonehenge, where it remains. As a spokesman for Pembrokeshire council remarked at the time: “Stone-age man never had the health-and-safety people looking over his shoulder.”

Facebook Twitter Pinterest Harry Shearer in character as Spinal Tap bassist Derek Smalls. Photograph: Daniel Knighton/Getty

Even leaving aside the innate absurdity of a nation spending three decades deciding whether or not to build a tunnel beside it, Stonehenge often operates as a magnet for the ludicrous. In the 1984 mockumentary This is Spinal Tap, the fictional rock band commissions a reproduction of the monument as a stage set, but there is a confusion between feet and inches. As a result, a comically tiny arrangement descends on to the stage. (Harry Shearer, who played Spinal Tap bassist Derek Smalls before finding greater fame as the voice of Mr Burns in The Simpsons, is one of the many people whose anti-tunnel views can be found on the planning website, where he writes as a member of the “admittedly fictitious band”.) The episode echoes the real events of Black Sabbath’s 1983 US tour, for which a vastly oversize Stonehenge set was accidentally produced owing to a mix-up between metric and imperial.

Indeed, Stonehenge’s massy blocks seem irresistible to copyists: a website, Clonehenge, charts replicas made of everything from cars and lava-lamps to vegetables and gingerbread. The most celebrated duplicate of recent times may be the artist Jeremy Deller’s lifesize version in the form of a bouncy castle, which he memorably described a “a way to get reacquainted with ancient Britain with your shoes off”. (Deller is anti-tunnel. “A nice idea, but it’s clearly not long enough.”)

In its time Stonehenge has been interpreted as temple to the sun, Boudicca’s tomb, Satan’s court, an observatory, a computer, a phallic device for symbolically impregnating the sun, and, fairly recently, as a place of healing – “the neolithic A&E unit for southern England”, as the theory’s proponent put it. (Perhaps it was inevitable that at some point Britain’s favourite monument should be imagined as prefiguring its most treasured institution, the NHS.)

Deller, who has followed his inflatable Stonehenge with a range of clothing including T-shirts adorned with mouths full of crooked megaliths and the caption “English teeth”, regards Stonehenge as a mutable, open-ended symbol of Englishness – like Jerusalem, a hymn that can be sung with equal fervour at socialist rallies and rugby tournaments. “Stonehenge is fluid – in the way that national identity is fluid,” he said. And, he argued, more necessary than ever. “As times become more uncertain, people look to the stones for a kind of truth,” he told me. “People want the stones to speak.”

Stonehenge is a mirror – it reflects back your obsessions. In the 1960s, astronomer Gerald S Hawkins argued that Stonehenge was an astronomical “computing machine” capable of predicting eclipses – a theory that held sway for decades, although now many of the celestial alignments he discovered are thought to be coincidental. A gynaecologist, Anthony Perks, writing in 2003, thought it was a fertility symbol in the shape of a vulva. (His article was titled The Vagina Monoliths.)

Some 17th- and 18th-century scholars were convinced Stonehenge had been built by the druids, a sect of rather frightening Celtic priests mentioned in Roman texts. This theory proved so heady that it inspired the creation of an actual, modern religion: druids began performing ceremonies at the stones in 1905, and still do. Unfortunately for the modern druids, Stonehenge is now known to predate their imagined predecessors by several thousand years. (Even so, it would be a hard-hearted person who entirely dismissed the modern druids. You don’t have to be a believer in ley lines to agree with them that the stones radiate a power beyond rational considerations.)

In fact, scholars are now convinced that Stonehenge can finally – after centuries of debate – be fixed at about 5,000 years old, after organic material excavated at the base of the stones was radiocarbon-dated in the 1990s. It is not easy dating such monuments – a fact demonstrated by the recent revelation that an unusual bronze-age stone circle in Aberdeenshire was actually built 20 years ago by a farmer.

Currently, the dominant theory about the purpose of Stonehenge is that of Mike Parker Pearson, who excavated in the area for several years from 2003. He hypothesises that it was a first and foremost a place built to honour the dead – and that the community that built it lived nearby, at Durrington Walls. For him, the inclusion of the Welsh bluestones was a gesture symbolic of some kind of “political unification” of disparate British peoples after a period of “neolithic Brexit” – a slow period of recession, some six centuries after the introduction of farming, when Britain’s ties with the continent were cut off.

In the early 1990s, Stonehenge was a mess. Tourists got to it via a grubby pedestrian passageway under the A344, the road nearest to the monument; the visitor centre and parking facilities were tatty; the annual solstice celebrations saw embarrassing clashes between travellers and law enforcement. When the Department for Transport first announced plans to improve the A303, it seemed – at least to the energetic new boss of English Heritage, Thatcher favourite Jocelyn Stevens – as if all of this could be tackled at once. But it wasn’t so simple. It took two decades for the A344 to be closed and grassed over and a new visitor centre opened. The problem of the A303, however, has proved even more stubborn.

The first proposal was a “cut-and-cover” tunnel (effectively, a trench with a lid), rejected after public consultation in 1993. The following year, English Heritage and the National Trust, which owns more than 2,000 acres of land around Stonehenge, announced that their preferred option was a deeper, bored tunnel of about two-and-a-half miles that would avoid disturbing the archaeology – but in 1998, the government declared this “unaffordable and uneconomic”. In 2002, the DoT unveiled plans for yet another tunnel, this time only 1.3 miles long – supported by English Heritage, but too short to satisfy the National Trust, which said it presented an “urgent, serious and imminent” threat to the landscape. Finally, in 2007, the scheme, the development of which had already cost around £20m, was dropped on grounds of cost.

Facebook Twitter Pinterest Photograph: Sean Smith/The Guardian

For the campaigners who had fought these projects for 15 years, it seemed like a victory. “In 2007, we thought we’d cracked the road scheme, but obviously not,” Kate Fielden told me over tea and cake in her pottery-filled cottage. A retired archaeologist and one of the leading lights of the tunnel resistance, Fielden first got wind of the revived tunnel scheme in 2013, when it was being eagerly promoted by MPs keen for a boost to the local economy. Her group, the Stonehenge Alliance, which had become something of a sleeper cell, snapped back into action, writing to ministers even before the new scheme was announced by David Cameron in December 2014. This time, the National Trust had been brought back on side by the promise that the mooted tunnel would be half a mile longer than in the previous scheme.

Then Highways England got to work, drawing a spaghetti of lines on a map to delineate possible “route corridors”, as the parlance has it. David Bullock is the project manager for the Stonehenge section of the A303 upgrade. The scheme, he told me when we met in October, “is in the hard-to-do bracket … not only have you the challenge of the world heritage site, to the north you have Salisbury Plain, the largest area of military exercise in the country. To the south, you have open very lush and ecologically rich areas, so it’s a very difficult environment with which to weave a highway system.” The Stonehenge section of the A303 was designed for 13,000-14,000 cars a day, “but you are squeezing through an average of about 25,000. And that can rise by about 30% at peak times.” The A303, he said, is “a problem, it has been a problem for 25 years, and it is spreading like a cancer across the local road network.”

After a public consultation in 2017, the 1.8-mile tunnel was named as the “preferred route” by the DoT – to no one’s surprise at all, given that it had been effectively announced in 2014. Objectors such as Mike Parker Pearson are infuriated by the decision not to simply reroute the road well to the south of the site – which Highways England argues could disturb untouched archaeology. “I have never seen a statement that sets out why the archaeology around a southern route might be important, or what that is based on,” he told me.

Meanwhile, Highways England commissioned dozens of exploratory surveys looking at water tables and archaeology, at congestion and pollution, at the flight path of bats and the population of the marsh fritillary butterfly, a process that has so far cost £40m. Some locals are aggrieved by the disruption caused by all this preliminary work – and feel ignored by the consultation process.

Facebook Twitter Pinterest Merlin, co-leader of the The Astronumerical Druid Order. Photograph: Jeremy Deller

“All the major decisions are taken by people deemed to be in positions of authority – like the National Trust, English Heritage and Wiltshire county council. But I’m just a farmer. I’m expendable,” Rachel Hosier told me in the kitchen of her farmhouse, a couple of miles south of the stones. Her land contains important ancient barrows and an RSPB reserve for the rare, eccentric-looking bird, the stone curlew. She told me there had been disturbances to livestock, work done at inappropriate times in the farming year, and material from investigations left on her land – she even holds up a zip-lock bag of flints left behind by one of the archaeological teams. (Highways England said that work was discussed in advance, damage to crops compensated for, and steps taken to prevent a reoccurrence of the mislaid flints episode. Public consultations did result in changes: to the location of the tunnel’s western portal, the line of the road, and to a local bypass.)

Icomos, the International Council on Monuments and Sites, which advises Unesco, reported in April 2018 that there would be “irreversible damage” if the scheme went ahead; Unesco’s own world heritage committee has said that the project would “impact adversely on the integrity and the outstanding universal value” of the area. The Stonehenge Alliance has submitted documents arguing that the scheme contravenes a blizzard of laws, directives and conventions, including the 2008 Planning Act, the World Heritage Convention, the Bern Convention on the Conservation of European Wildlife and the Birds Directive.

Among the other opponents are a number of readers of the Telegraph, who took to the paper’s letters page to protest that motorists would no longer glimpse the large field of pigs adjacent to the stones, on Hosier’s land. (Typical letter: “On our visits to Shepton Mallet, my wife always looks forward to seeing the porkers enjoying their freedom, roaming the vast field … a wonderful advertisement for British farming.”) The druid Merlin, co-leader of the The Astronumerical Druid Order, raised a similar objection: a tunnel would rob passing motorists of the view of the stones, one of the most famous sights in England.

One blustery, perishingly cold October day last year, English Heritage threw a celebration at Stonehenge marking the monument’s centenary in public ownership. In a little marquee, where dignitaries huddled out of the wind, was a large Stonehenge-shaped cake, over a metre in diameter, which the archaeologist Julian Richards judged to be “pretty accurate”. Off near the visitors’ centre was Deller’s work Sacrilege – his inflatable Stonehenge – on which enthusiastic children and archaeologists bounced. A darkly weird piece for brass instruments, by composer Matt Rogers, was performed inside the stone circle, as tourists looked on in faint bewilderment.

At one point a group of druids, their medieval-style robes flapping about to reveal 21st-century jeans and boots, passed around bread and mead – more like Church of England communicants than the human-sacrificing druid priests of Julius Caesar’s imagination. As a line of Gore-Texed visitors patiently queued for a cuppa, it was hard to imagine anything more English. The tunnel scheme had been submitted to the planning inspectorate the previous week, and was being discussed in tones – depending on point of view – varying from horror to resignation to relief.

The principle of preserving a “national heritage” in perpetuity can seem as though it has been with us for ever – perhaps because bodies such as the National Trust seem like such timeless bastions of middle England. In fact, the idea is fairly recent – and Stonehenge itself played an important role in its invention.

Facebook Twitter Pinterest Jeremy Deller on his bouncy castle replica of Stonehenge, called Sacrilege, in 2012. Photograph: Murdo MacLeod/The Guardian

For centuries, the monument has been a tourist destination; by the mid-18th century the classic trip was to combine it with Salisbury Cathedral, 10 miles to the south. They were “two eminent models of art and rudeness”, Dr Johnson wrote, the cathedral exemplifying sophistication and Stonehenge, primitivism. (This is also the tourist programme that the Russians accused of poisoning Sergei and Yulia Skripal were planning, so they said, before they were foiled by slush underfoot.)

Victorian Stonehenge was a place of day-trippers, bicycle outings, Sunday school jollies, cricket matches and concerts. The craze for the new discipline of geology saw visitors chipping chunks out of the stones for their collections (a stall rented out chisels). It was this popularity and accessibility, partly brought about by the railway boom, that began to imperil Stonehenge – and simultaneously forge the idea that it ought to be preserved for future generations.

For many decades, landowners had rejected the principle of a national patrimony that would threaten their property rights. But finally, the antiquarian and MP John Lubbock (the man who coined the terms “palaeolithic” and “neolithic”) succeeded in pushing through the Ancient Monuments Protection Act of 1882. Stonehenge was one of first 26 English and Welsh monuments “scheduled”, or protected, under the act. At the time, the land was owned by a local grandee, Sir Edmund Antrobus, who put a fence around the site and began to charge for entrance; he also tried, unsuccessfully, to sell it to the nation for the inflated price of £125,000.

As the first world war loomed, the army bought up tracts of Salisbury Plain to use for exercises; camps and hangars crept close to the stones. A military presence is still obvious to any visitor: Apaches and Chinooks can approach thunderously close. “Is this normal?” I recently heard a worried-looking overseas tourist asking a staff member, as curls of artillery smoke dissipated in the middle distance.

Facebook Twitter Pinterest A druidic ceremony at Stonehenge circa 1923. Photograph: Harlingue/Roger Viollet/Getty

By 1915, Sir Edmund and his heir were dead, and the estate was put up for auction. A local man, Cecil Chubb, had come to the auction (according to local legend) looking for some dining room chairs; instead he bought Stonehenge for £6,600. Three years later, he gave it to the nation. After the war, fears grew that the downs around Stonehenge would be built on, and in 1927 land nearby was bought by public subscription for the young National Trust, founded a dozen years earlier.

Among those who rallied to the new cause of protecting rural England from the tentacles of development was a group of young women who formed a kind of 1930s Pussy Riot. Ferguson’s Gang, as they called themselves, were masked, anonymous activists who went by codenames such as Bill Stickers, Granny the Throttler, Black Maria and Red Biddy. They raised money for the National Trust and handed it over in the form of elaborate stunts – concealing cash in a fake pineapple, or rolled up in a cigar, and gatecrashing grand events to present it.

At their very first meeting, on 26 March 1932, Ferguson’s Gang passed a resolution, later sworn as a solemn oath beneath the stones themselves, “That ENGLAND is STONEHENGE and not Whitehall”. The sprawling capital, the machinations of politics, the grinding wheels of bureaucracy – none of that was important. For them, the soul of the nation lay in the ancient, slumbering magic of Stonehenge.

In 2015, the Conservative government spun off English Heritage – the descendent of the government body that cared for monuments after the 1882 act – into an independent charity, earning its own keep. Its ability to do this is strongly dependent on Stonehenge, which brings in 21% of its annual income of about £112m and which, with its 1.5 million visitors a year, attracts a million more than the next-most popular site, Dover Castle. Kate Mavor, the organisation’s chief executive, told me she thought of Stonehenge as a publisher might a bestseller – a title that supports other, less lucrative, works. While entry is free for English Heritage and Trust members, it otherwise costs £17.50 to buy a ticket to Stonehenge. More than half the visitors are from overseas. A vast coach park at the site decants tourists who will often also take in Bath and Windsor on a day trip from London.

At the cafe, there is Stonehenge branded water, the bottle decorated with runes (a Germanic writing system irrelevant to the monument), and there is a brisk trade in rock cakes (get it?). The shop sells Stonehenge woollies, T-shirts, snowdomes, fridge magnets and jewellery. Visiting Stonehenge today does not offer much in the way of solitary communion with the eternal verities; this is heritage commodified within an inch of its life.

But the narrative that Stonehenge has been ruined by mass tourism goes back a long way. Even Samuel Pepys complained of being ripped off by shepherds and innkeepers. Jacquetta Hawkes’s book A Land, a classic work on British prehistory, was published in 1951, when visitors numbered only about 200,000 a year. “Cafes and chewing gum, car parks and conducted excursions, a sense of the hackneyed induced by post cards, calendars and cheap guide books has done more to damage Stonehenge than the plundering of some of its stones,” she wrote. “Men made it and men destroyed it.”

Who owns Stonehenge? Who gets a say in its future? Who is listened to, and who is ignored, in the making of these decisions? These are the questions that crowd round the monument – questions that are not so different from those that surge around the future of the British Isles themselves. Stonehenge is often regarded as a symbol of comforting longevity; of the persistence of deep antiquity against the insistent tides of more recent history.

But that is not quite true: permanence and certainty seem to bounce off its sandstone and dolerite surfaces. At the beginning of Rosemary Hill’s book Stonehenge, published in 2008, the author describes in two sentences what she regards as the only unarguable facts about the monument, including the name of the county in which it sits, its latitude, its proximity to the A344 and its management by a government-funded agency. But even some of these are already out of date: the road is gone and English Heritage is now a charity. Even the physical appearance of the monument has altered relatively recently. In 1797, and again in 1900, two of the great sarsen stones collapsed; they were re-erected after the first world war, and at the same time, other vulnerable stones stabilised in concrete. Further restorations were carried out in the 1950s and 60s.

Radiocarbon analysis conducted in the 1990s resulted in the monument becoming – more or less at a stroke – nearly 1,000 years older than previously thought. Stonehenge is not even, properly speaking, a henge. The term, coined by Thomas Kendrick of the British Museum in 1932, was adapted from the word Stonehenge (which probably derives from a Saxon word meaning “hanging rock”). But “henge” is supposed to describe circular monuments enclosed by a ditch inside a bank; Stonehenge’s ditch and bank are actually the other way around.

Facebook Twitter Pinterest Restoration work in 1958. Photograph: PA

Stonehenge, then, is not so much about solidity and eternity as confusion and internal contradiction. It is partly its quicksilver ungraspability as a sign that makes it so magnetic, so available to every generation. “Not a week goes past without a news story about Stonehenge, some discovery, some controversy,” said Jeremy Deller. It is this endless mutability of meaning that makes it, for him, “the most contemporary building in Britain”.

Many people lay claim to Stonehenge, from the charities who care for it, the archaeologists who study it, the druids who revere it, to artists like Deller who borrow its power to make meaning of their own. It resists ownership, but it is vulnerable, and not immune to human activity. Parker Pearson, whose research on the purpose and people of Stonehenge continues, talks of the world heritage site as a kind of island, on the fringes of which hover threats in the form of gradually encroaching development. In the north, there are 917 new homes for military families “debased” from the last cold war-era German garrisons. At the east, there are the glinting sheds of the new, bathetically named Solstice Park, an out-of-town business estate complete with a Costa, a McDonald’s and a Holiday Inn.

The tunnel project that Chris Grayling, or his successor, will soon approve or reject, is an example of a British compromise that even its most ardent champions find difficult to praise to the skies. The whole point of a road scheme, Highways England’s David Bullock told me, “is to take all those not quite good enoughs to make a good enough project”.

Heather Sebire, the English Heritage archaeologist with direct responsibility for Stonehenge, talks about how the experience of seeing the stones is at present horribly disrupted by the noise and pollution of the cars and lorries, by the twinkle of headlights at dusk and dawn; she believes the landscape around the stones could be so much better understood and appreciated by visitors without the dangerous, fast-moving A303 bisecting the downland. Even she, though, accepts it is not ideal. “It is difficult,” she conceded, “and the government is adamant it has funding only for a tunnel of a certain length. We have managed to stretch it a bit, and there have been other mitigating factors.” For Kate Fielden, who has fought such developments for 30 years, it is simply not worth it – in fact, it would be better to do nothing at all. “I don’t see why you should ruin a world heritage site and get to Exeter 10 minutes faster,” she said.

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According to English Heritage’s Kate Mavor, it is pointless to try to argue for a longer tunnel, because the money is simply not going to be made available. “The whole economic argument crumbles, and there has to be an economic argument for it to get to the top of the Highways England list,” she said. “If we were to push for a longer tunnel, the scheme would never happen. You have to balance the good versus the bad. In this scheme, the good, at the economically viable length for the tunnel, outweighs the bad.”

So it is that a plan no one can bring themselves to support wholeheartedly is trundling forward, despite many anxieties about the long-term consequences. Parker Pearson talks about previous incursions into the landscape around Stonehenge – the first world war camps, an old custodian’s cottage, the A344. “But all these things were undone. This is so enormous that it cannot be undone,” he said. “They will be blasting through the densest group of neolithic barrows anywhere in Britain. It’s going to affect the setting for ever.”

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