Judge it by its cover, and you might imagine that Dan Brown's The Da Vinci Code is just another trashy airport novel, with no greater claim to literary significance than as an untaxing way to fill a couple of empty hours on a plane. Yet in America, this conspiracy thriller has just displaced Robert James Waller's The Bridges of Madison County as the most successful hardback novel ever published. The print run currently stands at 6.2 million copies and rising.
This week it shot straight to the top of Britain's paperback fiction bestseller charts, with WH Smith reporting "frantic" sales; its publishers, Bantam, are confident The Da Vinci Code will be one of the year's top-five selling novels.
Rivals are already scrambling to cash in on its popularity, with a flood of spin-offs hitting the shelves this spring: Secrets of the Code: the Unauthorised Guide to the Mysteries Behind the Da Vinci Code; The Truth Behind the Da Vinci Code; and Breaking the Da Vinci Code - Answers to the Questions Everybody's Asking. So just what are these questions that "everybody is asking" and how has an apparently routine thriller, panned by critics for its lumpen prose style, achieved such dizzying commercial success?
The key lies in the obscure and ancient religious sect of Gnosticism. For as well as touching all the bases required of a mass-market thriller, The Da Vinci Code also gives readers what amounts to a history lesson on long-buried Gnostic writings that have hitherto been largely an academic preserve. Beguilingly, Brown presents Gnosticism as the twin sister that Christianity has kept locked in the cellars under St Peter's since the 2nd century because it could not stomach its freedom-loving, gay-friendly, anarchic take on God.
"If you've ever wondered about the roots of religion," writes one reviewer of The Da Vinci Code on Amazon in America, "you need wonder no more." "I will never look at the Last Supper in the same way," says another. "Mr Brown introduces us to aspects of Christianity that I had never known existed" is how a third fan puts it.
"I'm in no doubt as to why The Da Vinci Code has done so well in the States," says Elaine Pagels, Professor of Religion at Princeton, an expert on Gnosticism and author of Beyond Belief, an account of the Gnostic Secret Gospel of Thomas, also published this month.
"By going back to these Gnostic gospels that few have heard of until now, Dan Brown's novel raises an intriguing question in readers' minds: 'If we didn't know about the ancient writings he has used, what else don't we know about, what has been hidden from us or edited out by official religion?'. And that question is being asked at a time when many spiritually inclined people in America are profoundly disillusioned with authority in the churches - not least in Catholicism because of the paedophile priest issue.
"So Gnosticism has a very timely revolutionary appeal - the chance of achieving a sense of the spiritual, through a time-honoured channel, without the need for flawed churches and institutions."
If The Da Vinci Code has set off a stampede to rediscover the ancient Gnostic sect that lies at the heart of the book's plot, then there are also other signs in modern culture that this almost forgotten creed is making a comeback. Madonna and Britney Spears are just two of those who have been attracted by the mysticism of the ancient Jewish Kabbalah, itself heavily influenced by Gnosticism. Meanwhile Keanu Reeves' all-action blockbuster movie series, The Matrix, is, its devotees have argued in exhaustive detail, a Gnostic parable about finding a perfect world away from earth.
Gnosticism has also been identified, by the author among others, as one part of the inspiration for Philip Pullman's award-winning His Dark Materials trilogy. Philip K Dick, the sci-fi novelist whose works are currently top of Hollywood's wish list for adaptations (to follow in the footsteps of his Blade Runner, Total Recall and, most recently, Minority Report), was reportedly obsessed with Gnosticism. And as the ultimate endorsement, Time magazine has run a cover story on the sudden popularity of Gnosticism and how "more and more people are turning to [its] ancient texts to develop their own religious rites".
The Gnostics - from the Greek word gnosis or knowledge (hence agnosis, or lack of knowledge) - existed at the birth of Christianity. No historian has ever felt confident enough to say which of the two came first. And for almost 200 years following Jesus's death, Gnostic views were as influential as those which we now associate with mainstream Western Christianity.
The Gnostics believed that individuals could attain mystical knowledge through divine revelation. They were a holy, impractical bunch who largely rejected this world as flawed - some saw it as the creation of the Devil - and so sought through asceticism, celibacy and fasting to hasten death and reunion with God. They recorded their revelations from above in a series of gospels about Jesus's life which told a very different story from the official versions found in the New Testament, and which were destroyed when the Gnostics were suppressed as heretics by the church fathers at the end of the 2nd century.
However, in 1945 at Nag Hammadi in Upper Egypt, an ancient jar was unearthed containing Gnostic gospels. It is on these texts that Dan Brown bases the denouement of his plot. According to his novel, the Gnostic Gospels of Philip and Mary show that Jesus and Mary Magdalene were lovers (though this interpretation is disputed), and fearing that the revelation of this fact would destroy the Church, the Catholic establishment has carried out a series of murders to keep the secret from leaking out.
There is a certain historical justice in Brown's suggestion that the Catholic Church has been willing to kill to stop people hearing about Gnosticism. The Cathars (or Albigensians) in southern France in the 13th century were Gnostics who rejected the trappings and intrigue of organised religion; who (unlike Catholicism) treated men and women as equal before God; who had few of Christianity's hang-ups about sex; and who stood apart from the materialism, politics and corruption of the world, seeing it as the work of humankind, and sought a higher, purer way of life. Rome so feared the good example that the Cathars offered that it condemned them as heretics and set up the Inquisition to kill them off and write them out of the authorised version of history.
But you can't keep a good story down, and the broadcaster and novelist Kate Mosse is among those riding the Gnostic new wave. Her Cathar-based novel, Labyrinth, set for publication in 2005, was sold at auction after a fierce bidding war among publishers.
"I do feel," says Mosse, "as if there is something bigger going on now around the whole question of Gnosticism. There's an element of us, confronted by the state of our world, finally abandoning the linear view of history - that humankind has simply got better and better at things - and instead searching through the past for guidance, for wonderful flowerings and movements that seem to understand our needs so much better than anything else currently on offer.
"I see Western society right now as being in search of something enduring to believe in, something with potential to raise our eyes to the horizon at a time of war, religious hatred and what seems awfully like a new crusade. And Gnosticism, I think, offers the possibility that the answer is there within us and always has been."
However, the award-winning author Michèle Roberts, who has also written about the Gnostic Cathars (in her novel The Wild Girl), sounds a note of caution about this latest renaissance. "I'm glad to say I thought myself out of Gnosticism about 20 years ago. Back then I could see its attraction - feeling free of any institutional constraints on being spiritual, a way for ordinary people to seek divine enlightenment. But if the new adherents get beyond the desire to look groovy and radical and really start looking at what Gnosticism was all about, they are in for a nasty shock. The Gnostics split spirit and matter, and saw matter as evil. They believed that men were spirit and women were matter. So, yes, there may have been some Cathars who allowed women a role - usually only after they had had sex with an enlightened man - but at heart Gnosticism was profoundly anti-woman and one of its greatest influences on Christianity was to make it the same."
So beyond the initial thrill for The Da Vinci Code readers or Matrix Reloaded viewers of discovering this skeleton in Christianity's closet there lie some unpleasant choices if they want to take on board Gnosticism with the traditional zeal of a convert. The bottom line is its demand that you reject everything to do this world as flawed and evil - homes, cars, money, all that is matter, not spirit.
It is quite a challenge. There was always a pessimistic, bleak, almost manic, streak in Gnosticism. That is why the early church fathers tried to bury it because they realised it had nothing invested in continuing this world. And potential new converts might also like to ponder the example of the Bogomils, a Bulgarian Gnostic cult in the 9th century. It insisted, in line with Gnostic beliefs, that sex for procreation was the work of the Devil, as it only served to prolong a world that was a vale of tears. So all its adherents, if they wanted to make love, were only allowed to bugger each other.
Given such strictures, it is perhaps unsurprising that, despite the numbers of those expressing a fashionable interest in Gnosticism or the history of the Gnostic gospels, there are few actually signing up. Not that this anti-institutional philosophy has ever been much given to organisation. The handful of UK-based Gnostic movements is apparently so otherworldly that they don't answer their phones, if indeed they have such evil contraptions. And those with a presence on the web seem more concerned with using Gnosticism to bash the church. The Gnostic Friends Network is a virulent anti-Christian outpouring, headlined "Jesus Says Love Your Enemies". It takes the Gnostic belief that this world was the work of the Devil and turns it into a charter for Devil-worshipping that has the shrill sensation seeking of a latter-day Aleister Crowley.
Mandeans are the only surviving traditional Gnostics, with no more than 20,000 adherents living in southern Iraq and south-western Iran.
The tendency to use the term Gnosticism loosely to sum up a widespread disillusionment with organised religion has persuaded Professor Elaine Pagels for one to abandon the term altogether as hopelessly corrupted. Other academics have followed suit. For a more populist audience though, as the phenomenon of The Da Vinci Code spreads around the globe - a Hollywood film deal has already been signed - Gnosticism will doubtless have its 15 minutes of fame as shorthand for the age-old yearning for there to be something more to this world than meets the eye. As an enthusiastic reader from New York tells other Amazon readers about Dan Brown's book: "It will only take you a few hours to read and it changes your entire perspective on religion, the church, and life."
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'The Da Vinci Code' by Dan Brown is published in paperback by Bantam. Elaine Pagels' 'Beyond Belief' is published by MacmillanReuse content