Its authenticity might be in doubt, but it's hard to deny the Turin Shroud's near-miraculous powers of longevity as the Catholic Church prepares once again to roll out the world's most famous relic – and to cash in on the unique mixture of devotion, speculation and ridicule that it generates.
This spring the millions of visitors shuffling up the aisle of Turin cathedral will gaze on what is purportedly the burial cloth of Jesus through a secure, climate-controlled case.
But it wasn't always so carefully protected. Hauled to and fro across the Alps, scorched with molten metal and draped ostentatiously over temporary balconies by Savoy kings only to be unceremoniously whipped back in at the first sign of rain, the cloth has needed the backing fabric roughly stitched to its underside to avoid complete disintegration.
As recently as 1997 it narrowly escaped incineration in another fire, and it wasn't until 2002 that restoration experts were finally able to remove the clumsy patchwork repair done by medieval nuns.
But the relic's potent yet ever-morphing symbolism is more interesting than its physical vicissitudes. In addition to supposedly being His burial cloth, the Shroud has been the standard-bearer for a religion, a source of political and religious prestige, a creator of wealth and, most controversially of all, evidence, say some, of the divine event that underpins the Christian faith. Over the ages and right up to the present day, for bishops, kings, politicians, true believers and of course, conspiracy theorists, the Turin Shroud has been manna from heaven.
Today's enterprising Torinesi have not been slow to pick up on the miraculous economic properties of "La Sindone", as the Italians call it.
Traditionally, a public display of the Shroud, or an "ostensione", occurs once every 25 years. But just 10 years after the last exhibit the Vatican, which has owned the Shroud since being bequeathed it by the now-defunct Italian Royal Family, has accepted the city's assertion that a six-week public display, to attract visitors from around Italy and beyond, would provide a welcome fillip for an industrial city hit harder than many by a vicious recession.
Not for the first time in the Shroud's history, an element of vanity emerges. The exhibit will enable the city's current archbishop, Severino Poletto, to retire this year basking in the relic's sepulchral glow. Fiorenzo Alfieri, Turin's refreshingly matter-of-fact councillor in charge of cultural events, makes no bones about why La Sindone is being wheeled out again in 2010: "Cardinal Poletto wanted to conclude his tenure with a display of the shroud."
And of course there's the money. Town Hall bean-counters estimate that Shroud day-trippers will contribute €121 a head to the city's economy, while those who stay over will spend €215 each day.
So far the omens are good. More than a million advance tickets are booked, and estimates of total attendance over the six weeks from 10 April to 23 May range from two to four million. The viewing is free, but the bookshops and merchandising – and nine makeshift confessionals – are being readied to welcome them. Visitors will be led via a new side entrance, past the ruins of a Roman amphitheatre, into Turin's pale cathedral. This is an understated Renaissance building, stranded in a bleak piazza, and surrounded by a sea of Baroque, but Turin's dazzling architecture is likely to be the last thing on people's minds as they queue for their five minutes (maximum) to scrutinise, revere or possibly turn a blind eye to the oddness of the Shroud.
Who are all these visitors? "A lot of day-trippers, but also people from around Italy and many foreigners," explains Alfieri. "About seven per cent are from abroad. French, Germans, Spanish, Americans, Poles. The most devout though are the Russians; they don't stop and think about whether it's real. For them there's no question, it's an icon."
In the age of Dan Brown and Da Vinci-mania the story of the Shroud is also the perfect potboiler, with something for everyone – including amused sceptics who'll appreciate its cameos from the Knights Templar and even the Renaissance man himself.
Some claim there is evidence that the Shroud was kept and revered as early as the 6th Century. But sticking to the established facts, the first reliable documented evidence of the Turin Shroud came in the mid-14th century when the French crusader Geoffroy de Charny claimed to have brought the cloth back from the Middle East, before displaying it in a church at Lirey, 100 miles south-east of Paris.
In 1453 it became the property of Duke Ludovico I of the House of Savoy, who moved it to Chambéry. A few decades later, in 1532, it was almost destroyed by a fire in its chapel. The silver box in which it was kept began to melt in the fierce heat, causing the distinctive symmetrical, butterfly burn-holes right through the folded cloth. With the best of intentions, nuns in charge of the cloth made matters worse by sewing patches into some of the gaps.
The Savoys moved it to Turin in 1578, and in 1694 placed it in their private chapel between their palace and the cathedral.
Thus the Shroud became a sort of divine mascot of the showboating Savoy household – the ultimate vanity relic. When members of the royal family wanted to remind themselves of their own piousness or importance they had merely to pop through the special Shroud Gallery into their own chapel to gaze solemnly upon the face of The Lord. And when the Savoys wanted to remind the plebs who they were, it was put on display in the open air – weather permitting – hung from specially constructed wooden stands. Ironically, though, the Savoys trampled all over the only thing that that could indisputably be said to date back to Roman times, the amphitheatre next to the cathedral, as they built an extension to the Royal Palace.
The Shroud's next big surprise came in 1898 when a lawyer, Secondo Pia, was given permission to take photographs of it, and it appeared that the "negative" formed by his huge, primitive camera of the human image was in reality the positive image – the true representation of the human subject "recorded" by the Shroud.
Shroud supporters insist that the positive image depicts a more realistic face than the ghostly, implausibly northern-European features seen from the faint, rusty-orange negative image on the shroud itself.
But attempts to build further on the discovery, by making three-dimensional models from the positive image, which were trumpeted again on 12 March, appear self-defeating; the resulting rather peculiar faces on display in Turin's shroud museum have more than a hint of Easter Island about them. And even Dan Brown would have problems making that work.
Scientific advances did bring other important insights, however. Most famously, and as it turned out, almost disastrously for the Shroud industry, the Vatican allowed research groups from Oxford, Zurich and Tucson to snip bits of the cloth's edges in order to perform carbon-dating tests.
The results, published in 1998 in the research journal Nature, appeared to spell curtains for the Holy Shroud. Each of the three independent research centres estimated that the Shroud was made between 1260 and 1390 – and was therefore nothing more than a medieval hoax, albeit a cunningly constructed one, with an almost miraculous eye for detail.
A close examination the Shroud reveals what appear to be haematomas – swellings – on the right side of the face. The nose appears fractured. Chemical tests indicate the presence of blood stains, although sceptics claim they might iron-oxide salts daubed on. Undeterred, more enthusiastic researchers have even claimed that the bloodstain created by the posthumous lance wound shows evidence of serum separation that you would expect with blood loss from someone who was already dead when the wound occurred. And to the surprise of many, despite the apparent knock-out blow from the Nature paper, the Shroud story has showed some signs of a resurrection.
In 1999 a botanist at the Hebrew University of Jerusalem announced that he had found pollen grains on the shroud from plants that could only be found in the Holy Land.
But more significantly, in January 2005, came the news that really gave the Shroud industry a new lease of life. A retired chemist called Raymond Rogers, formerly of the Los Alamos National Laboratory in the US, produced in another science journal, Thermochimica Acta, evidence that 1998 carbon-dating result had been botched because the researchers had tested patches contaminated with material used to repair the medieval fire damage. This has been disputed.
Nonetheless, his much-publicised estimate suggested that, based on the degree of decomposition of the chemical vanillin, the Shroud was between 1,300 and 3,000 years old. Shroud believers were exultant.
Scratch below the surface, though, and Rogers' claim to be a neutral observer, or even a Shroud-sceptic, soon crumble. He has published other pro-authenticity papers, and is a member of pro-authenticity Shroud of Turin Research Project. And other scientists raise their eyebrows at the mention of Rogers' vanillin-dating method. Luigi Garlaschelli, a University of Pavia chemistry professor who last year claimed that Shroud-like images could be made by rubbing a linen-covered mask with acid-containing pigment, says Rogers' technique "is not any way a reliable method for estimating an object's age".
But following Rogers' paper, Shroud believers now had the bit between their teeth and swatted aside these concerns. They received another boost last year from the Vatican's very own Indiana Jones, its medieval history researcher Barbara Frale, who seems to perform the Shroud-waving duties that the Church's upper echelons carefully avoid.
In April she brandished documents from the Vatican's Secret Archives which she said suggested that the Shroud had been secretly kept by that other staple of a good conspiracy yarn, the Knights Templar (a claim that incidentally seemed to dispel even-more-fanciful assertions that the Shroud was an self-image painted by ... you guessed it ... Leonardo).
But following suggestions by a French scientist that the Shroud contained traces of words in written Aramaic, Frale was on the case again. She told Vatican Radio in July that her own studies suggested the letters were written more than 1,800 years ago.
Then in November she announced that from the partially legible Aramaic words – written, she said, in a manner consistent with the cloth's supposed ancient Palestinian provenance – she had been able glean the text of a death certificate – containing it turned out, an almost suspiciously replete description of events: "In the year 16 of the reign of the Emperor Tiberius Jesus the Nazarene, taken down in the early evening after having been condemned to death by a Roman judge because he was found guilty by a Hebrew authority, is hereby sent for burial with the obligation of being consigned to his family only after one full year."
You could almost hear the Carmina Burana cantanta from the Old Spice advert blaring as she gasped: "I think I have managed to read the burial certificate of Jesus the Nazarene, or Jesus of Nazareth." She included this claim in her book La Sindone di Gesu Nazareno (The Shroud of Jesus of Nazareth).
While researchers such as Frale least offer some evidence for their claims, another section of the Shroud research industry has morphed into something other-wordly, producing essays and papers that would have scriptwriters for The X-Files shaking their heads in disbelief. What these theories lack in credibility, however, they more than make up for in ambition.
In oddball conferences, and in the pages of obscure research journals, philosophers, scientists and various self-proclaimed experts say that the Shroud is also that Holy Grail of theological research – physical evidence that the pivotal event in Christianity, the Resurrection, actually occurred.
The gist of their argument is that if regular science can't explain how a dead man left such an enduring negative image of himself on a sheet of linen, something extraordinary must have occurred – quite possibly a release of nuclear energy as the Son dematerialised and went back to whence he came.
At a Shroud conference in Orvieto in Italy in 2000, philosophy professor Phillip Wiebe, from Trinity Western University in Canada, discussed the theory proposed by various physicists and chemists that – and concentrate, this is the science bit – the "strong nuclear force within the atoms comprising the body of the Man (in the Shroud) was simultaneously turned off", allowing "freed subatomic particles" to leave their "imprint" on the cloth.
Mainstream experts are dismissive of the sci-fi brigade. "All-too often there are scientists who want to play the role of theologist, and theologists who want to be scientists," sniffs Gian Maria Zaccone, scientific director of Turin's Shroud Museum.
"Scientists can't explain how the image was formed, and we should leave it at that. It's not important whether or not it's a fake – the important thing is that it encourages faith."
But does anyone really believe in the Turin Shroud? Among the more credible experts, Zaccone comes closest to committing himself.
"I believe that there is much scientific evidence to suggest that La Sindone is the shroud of Christ," he says.
Until now, resourceful true believers have always managed to rustle up some kind of response to awkward questions. Thus the Shroud figure's apparent height – around 5'11" – which would have been unusually tall for a Palestinian of 2,000 years ago, and his rather European features might be explained by claims there were fairer-skinned people of such physique in Palestine in that period. The figure's seemingly elongated fingers have been explained by the presence of a skeletal disorder. But the formation of a three-dimensional image formed by a sheet laid flat on person's face? The Lord works in mysterious ways.
Dr Tom Verdon, an art historian and a canon who preaches at Florence Cathedral, concedes that if scientific studies were one day to prove beyond any reasonable doubt that the relic was a hoax, then the Catholic Church should be willing to admit it.
Other church figures, such as Monsignor Giuseppe Ghiberti, the president of the Turin archdiocese's commission on the Shroud, adopt, in true Vatican tradition, a more Machiavellian approach. Although Ghiberti has said the Vatican might consider a new round of scientific tests after the spring display finishes, it appears that there is only one result he is interested in.
The Church would not be obliged to concede it's a fake because "the church has never said it's definitely real", he says with a slight twinkle in his eye, before quoting some ambiguous words on the subject from John Paul II, the Pope who got plenty of mileage out of the alleged sightings last century of the Virgin Mary – Our Lady of Fatima – in Portugal.
The Shroud should provide some much-needed sustenance for John Paul's successor, when he makes a personal appearance on 2 May. Benedict XVI, with his penchant for red leather papal slippers and ermine-trimmed camauro cap, is as much a traditionalist as his predecessor.
But although he might share John Paul's belief in conservative doctrine, he doesn't possess his mentor's PR nous or communications skills, as seen by his jaw-dropping criticism of condom use in Aids-ravaged Africa, or his inflammatory statements on Islam.
In addition, the Vatican is labouring under accusations of money-laundering, gay prostitution rings, and most disastrously, of concealing widespread paedophilia among priests, following the explosion of abuse scandals in Ireland, the US, Australia, and now Germany. Whispers in southern Europe are now asking how long it will be before a similar scandal there dispels the tacit assertion that this sort of thing doesn't happened outside the Anglo-Saxon world.
With all this brewing, the Shroud should prove a welcome distraction from Easter onwards.
But could there even be doubts about something as seemingly innocent as the pilgrimage to Turin?
Just last month a Vatican theologian warned that veneration of relics ran the risk of replacing authentic faith with irrational superstition in order to "compensate for empty churches". Monsignor Pietro Principe's comments came as pilgrims began queuing to pray before the 13th-century remains of St Anthony of Padua.
The Sceptical Shroud of Turin website is, predictably, more damning: "The Shroud was created by an artist to lure faithful 14th-century pilgrims to visit a relic displayed for the purpose of supporting their religious faith and encouraging their monetary offerings. This unfortunate and unethical practice continues in the 21st Century."
But there's also a feeling that some of the professional sceptics – in the manner of outspoken atheists – are shriller and more obsessive than the supposedly overly-credulous they've set out to defeat.
Twenty minutes' drive outside Turin lies the recently restored Venaria Reale palace, "Italy's Versailles". Here Dr Verdon is planning an art exhibition with important loans from around the world. As part of several major events in Turin to coincide with the Shroud exhibition, his show will focus on the depiction of Jesus in painting. In the exquisite setting of the palace's ballroom, Dr Verdon – a calm but imposing figure – insists that the Shroud exhibit is a good thing, which will underline for the faithful that Jesus "lived and died".
For a moment his gaze appears to focus through the windows on to the distant snow-capped Alps before he turns to me again. "I don't by inclination believe the Shroud is genuine," he says. "I can see all the historical problems with it. I think that the majority who come to see it will inside have their own very major doubts.
"But nevertheless they feel they need to go and see it, to join the thousands of others who have stood in line down the ages. And whether it's real or not doesn't change the fact that when I look on the Shroud I find it extremely moving."
The truth is the Shroud can be whatever you want it to be. And there will be very many people, probably more than a few undecided among them, who hope that science's knockout punch never actually lands.
The Shroud of Turin is on display 10 April to 23 May at Turin Cathedral, Italy
Shrouded in mystery: The relic's past
* Documented history of the Shroud begins in the mid-14th Century when French Knight Geoffroy de Charny displays it in Lirey
* In 1453 the Savoy family takes control of the Shroud, moving it to Chambery
* In 1506 Pope Julius II approves it as a public cult and gives it liturgical recognition
* In 1532 it is damaged by a fire in the Chambery chapel
* In 1578 it is moved to Turin so the Archbishop of Milan does not have to walk across the Alps to see it when he makes his pilgrimage on foot to give thanks for the end of the plague
* In 1694 the Shroud is moved to the Guraino Guarini-designed chapel between Turin cathedral and the royal palace
* In 1898, photographer Secondo Pia reveals true "positive" image of the Shroud for the first time
* In 1983 the will of Umberto II of Savoy leaves the Shroud to the Vatican
* In 1988 carbon dating suggests that the Shroud is a mediaeval forgery
* In 2005 a chemist disputes the carbon dating and suggests the Shroud is between 1,300 to 3,000 years old
And what, exactly, is it?
* A herringbone linen cloth 4.42 metres long and 1.13 metres wide, venerated as the burial cloth of Jesus Christ
* It appears to show the front and back impression of a bearded man with long hair
* The body appears to bear numerous injuries consistent with crucifixion, plus a gash in its side, consistent with the lance-wound suffered by Jesus
Body of evidence: Turin Shroud theories
Around the 6th Century AD, half a millennium after his death, the face of Jesus began appearing in art in the Middle East, from Turkey across to Syria. Many shroud experts, such as Gian Maria Zaccone, scientific director of Turin's Shroud Museum, say the image of Christ that suddenly emerged in that period bore a consistent and remarkable similarity to face on the Turin Shroud.
Equally significant, say some believers, are the reports dating early from the first millennium AD, of another cloth bearing the face of Christ. This legendary relic, the Mandylion of Edessa (named after Edessa, the Turkish town), is mentioned from the 6th Century AD onwards; some believers claim it and the Turin Shroud may be one and the same. Sceptics and the undecided say there are more holes, or at least gaps, in this theory, than in the Shroud itself.
"The Mandylion-Shroud connection is just a theory. I wouldn't want to bet on it," says Tom Verdon, a priest and art historian at Stanford University's programme at Florence.