In 1974, after months of planning and with the help of a team of co-conspirators, Philippe Petit infiltrated the World Trade Center and took a stroll between the two towers - 110 storeys up on a tightrope. He tells Donald Clarkeabout committing the "artistic crime of the 20th century"

FOR MOST people old enough to remember 1974, Philippe Petit's illicit high-wire walk between the towers of the World Trade Center was just one of many novelty "And finally..." stories covered by News at Ten. It got filed away with the dog who could say "sausages" and that streaker with the policeman's helmet over his privates.

More than three decades later, Man on Wire, a superb new documentary from James Marsh, reveals the astonishing truth behind this unusual adventure. Partly a heist movie, partly a wistful eulogy for a vanished epoch, the film explains how Petit, an eccentric French magician and street performer, spent six years planning a stunt that, even now, defies belief.

"Yeah. My response was the same as yours initially," Marsh, a good-looking Englishman in his mid-40s, tells me. "I was dimly aware of this event just as a piece of exhibitionism. It was a very beautiful thing in itself. But when you begin to look into it, you realise it was this extraordinary criminal conspiracy. Eight people were involved in an amazing scheme."

Indeed. Petit and his collaborators posed as architectural journalists to get access to the top floors of the buildings, then still under construction, and took photographs of ledges, access points and hiding places. On the afternoon of August 12th, 1974, they split into two teams and concealed themselves beneath tarpaulins on either side of the chasm above New York. The next morning, after using a bow and arrow to fire a string from one building to the other - the string was attached to a rope and the rope was attached to a cable - Petit stepped confidently from the 110th floor and into history.

"It is a different business crossing a wire at that height than it is crossing at, maybe, 10 storeys," Petit says. "You die if you fall from either, of course. But you are more exposed at 110 storeys. Also, the void is so great it becomes almost inhuman. It is so great it becomes a monster ready to devour you. That is what happens when you are a human confronted with something of that magnitude." Petit, now a sprightly 57, still looks very much as he does in the copious archive footage Marsh gathered together for Man on Wire. A furious talker with an inexhaustible passion for subversion, he now lives in New York state and, in between his duties as artist-in-residence at the Cathedral of St John the Divine in Manhattan, he still finds time to practise circus skills and magic.

In the film, he traces his taste for breaking rules to a strict upbringing by inflexible parents. "I think that probably is right," he gabbles in his fluent, slightly eccentric English. "My father was a military man and had a very strict way of talking to me. I had a hard time with that. I hardly talked to my parents. In a strange way, I reacted against all that and became a street juggler and a performer. When, as a kid, I was told, 'Stop doing that! Come to dinner,' I would keep doing whatever it was on principle. When somebody says, 'Don't go there', I get interested and that becomes the only place I want to go."

As a teenager, Petit taught himself how to be a pickpocket and has recently written a book on the topic. From time to time, he refers to himself as a criminal, but it seems this is yet another act of cheeky provocation.

"I am an artist and so maybe I am a criminal artist. Some people, after I crossed the World Trade Center, said this was, maybe, the crime of the century. Well, perhaps. But I didn't steal anything. Nobody got hurt. So that hardly seems fair." Petit's first great act of artistic criminality came in 1971 when he walked between two of the spires at Notre Dame Cathedral. He later crossed a section of Sydney Harbour Bridge, so by the time he attempted the World Trade Center operation, he had already perfected many of the necessary techniques.

The spark for the idea came during a visit to the dentist in the late 1960s. While browsing through the magazines in the waiting room, Petit happened upon an article describing two enormous buildings that were soon to be built in New York. The possibilities for mischief were immediately apparent.

"I was just 18 at that time," he says. "I saw a photo of the model of the towers. I didn't work on it day and night for six years, of course. But the idea would come back to me when I read something about it. When I eventually read they were near completion, then I knew it was time to move, because it would be much easier before they were properly finished. It would be easier to get in. I went there and spent maybe eight months doing spy work."

Marsh's furiously exciting film, which blends reconstructions with original footage filmed by Petit, tracks down many of the collaborators who helped plan the operation. One of the many questions that spring into one's mind concerns the matter of how on earth these apparently sane people - most of whom remained on good terms with Petit - were persuaded to embark on such an unlikely scheme. If an eccentric young Frenchman approached you and suggested breaking into the city's tallest building for a spot of circus-related fun, what would you do?

"You must remember that, after Notre Dame, there was a front-page picture in all the newspapers of the world. 'Here is the newly born poet of the high wire' and so on. There was a little wave of celebrity. I was able to show them this scrapbook and show that I was not completely crazy. Later, I became a kind of folk hero to New York."

In these days of aggressive security and intrusive surveillance - much of it inspired by later, less happy events at the Twin Towers - it is cheering to discover how tolerant the New York authorities were of Petit's adventure. When he was eventually persuaded to come off the wire, he was, of course, arrested, but the charges were eventually dropped on the condition that he stage a show for the city's children.

Though New York did warm to Petit, many declared themselves bewildered by his refusal to explain in one-syllable words why he attempted the walk.

"Why? Why? Why?" he says with Gallic shrugs. "Always this question." Maybe he wanted money. Maybe he wanted fame. Maybe he just liked showing off.

"No. I don't care about money or fame, except that they help me to do more exciting things," he says. "And for me there is not an ounce of showing off involved. When I hear that phrase, 'showing off', I think of an imbecile. I think of somebody who is not profound, but wants to be recognised for his prowess. I was a man of the theatre who wanted to create a bridge and turn a man-made place into a theatre.

"I am not attracted by silly actions. I am attracted by a more profound path. If I were a sculptor, I would work in clay. I work in space."

Unsurprisingly, Petit has spent much of the last 30 years fielding offers to make films of his life story. But, as he explains, most producers suggested deals that merely required him to accept a nice big cheque, keep his nose out of the production and then turn up smiling at the premiere. James Marsh, creator of the acclaimed 2000 documentary Wisconsin Death Trip, made it clear that, while the director would retain final cut, Petit would be consulted throughout the production.

The result is one of the year's most riveting entertainments, but many viewers will find a particular topic conspicuous by its absence. Marsh has wisely decided to make no direct reference to the events of September 11th, 2001. That unspoken sadness adds a sombre quality to even the happiest moments in Man on Wire.

"I was in New York that day," Marsh explains. "I actually filmed some of the footage that later appeared on the BBC. When it came to making the film, I was clear that I didn't want those events mixed in with what was a essentially a caper movie." He does, however, include a photo of Petit crossing the wire while an aeroplane flies overhead. The juxtaposition of aircraft and skyscraper is momentarily startling.

"It was just one of the best photos showing the scale of the achievement," Marsh says. "But why should we allow those buildings to be remembered for just one reason? The reasons for showing it are more compelling than those for not showing it. It became a matter of principle: I will not let what happened 30 years later affect my depiction of this great moment."

Petit has a few small complaints about the picture - he hates the contemporaneous pop music, for example - but, on balance, he finds it a very satisfactory piece of work. Inspired by the experience, he has recently signed a deal with Robert Zemeckis, director of Back to the Future, to develop a dramatic feature based on his life.

It sounds as if the artistic criminal may be joining respectable society.

"Well, I try to behave more now," he laughs. "But, you know, when I see a sign saying 'don't step on the grass', then that is still the only place I want to step."

Man on Wire opens today. Click on the related link (right) for the Ticket's review.