"If I'd had to climb down to Hell itself and wrestle the film out of the claws of the Devil, I would have done so"

And little wonder. Two years into pre-production, the Sisyphean tale of a charismatic rubber baron who dragged his steamship over a mountain was beginning to resemble a dark metaphor for the process of filmmaking itself.

Every inch of progress had been a battle. Before a single frame was shot, location work deep in the Peruvian jungle was plagued by newspaper smears from international campaigners convinced (wrongly) that the indigenous extras were being exploited. Then their purpose-built production camp had to be evacuated following the outbreak of a border war with Ecuador. It was later burned to the ground.

Undeterred by this inauspicious start, the legendary creator of Aguirre: The Wrath Of God and Nosferatu The Vampyre tried again. Assembling his cast in the jungle outpost of Iquitos in 1980, he had completed 40 per cent of principal photography when his leading man contracted amoebic dysentery. Too ill to continue, Jason Robards left the director with months of now unusable film.

"When I returned to Germany to try to hold the investors together they asked me, How can you continue?'" Herzog would recall. "Do you have the strength and the will and the enthusiasm?' And I said, How can you ask this question? If I abandon this project I will be a man without dreams and I do not want to live like that. I live my life or I end my life with this project."

He could never have predicted how literally those words would come back to haunt him. In the months that lay ahead his cast, crew and a 1000-strong crowd of indigenous extras would encounter inter-tribal warfare, a drowning, two plane crashes and threats of murder. But for now it was casting problems that bit hardest.

The loss of Robards forced the departure of one Mick Jagger, now unable to reprise his remarkable early performance as Fitzcarraldo's "retarded actor sidekick" due to an impending world tour with the Rolling Stones.

"Losing Mick was, I think, the biggest loss I've experienced as a director,"

claimed Herzog as recently as 2001, explaining his decision to write the character out rather than recast. "I liked him so much as a performer that any replacement would have been an embarrassment."

But who would play Fitzcarraldo? The character so closely mirrored the ego and ambition of the director that for a time Herzog himself considered stepping in. Thinly based on Jose Fermin Fitcarrald, a Victorian rubber baron with a private army of 5000 men and a territory the size of Belgium, he was in one sense "just another ugly businessman". But Herzog's interest had been sparked by the tale that he had once dismantled a boat, carried it overland from one river to the next and reassembled it to continue his exploration. "Suddenly I had my story, not a story about rubber, but one of grand opera in the jungle with these elements of Sisyphus," he explained in the book Herzog On Herzog (2002). His Fitzcarraldo would be more bohemian than businessman, bent on funding an opera house in the jungle by exploiting otherwise unreachable rubber plantations. And his 340-tonne steamship would be dragged over a hill in once piece an almost impossible task for both protagonist and director alike.

"This is a film that challenges the most basic laws of nature," explained Herzog, who refused to use models or special effects. "Boats just are not meant to fly over mountains. Fitzcarraldo's story is the victory of the weightlessness of dreams over the heaviness of reality."

Today, roving the heat-thickened back streets of Iquitos, one can imagine the local response to the filmmaker as he explained his fantasy. Accessible only by river or air, with rainforest 600km all around, this town of 400,000 people is not known for German levels of efficiency.

Yet the former rubber boomtown must have been the perfect starting point for a post-colonial eccentric. In the central plaza, motor rickshaws endlessly circle the remarkable iron house designed in France by Gustav Eiffel and brought in up the Amazon piece by piece. Down at the water's edge, river taxis and the occasional drugs mule tout for passages to Colombia.

"This whole city is really just one big movie set," says Paul Wright, an amiable Californian entrepreneur who helped Herzog and his crew on their arrival. We're picking our way through a waterside market, where barefoot women sell the limbs of caiman from fly-blown market stalls, and men launch fishing boats from shacks on stilts above the water. "This district hasn't changed at all since Victorian times," he says. "It's just what Fitzcarraldo might have seen, still poor and dirty as can be."

Herzog, surveying the scene from his office on the far side of a swamp, pictured his hero listening to opera on his gramophone in a stilt house peopled by inquisitive Indian children and a pig. Meanwhile he commissioned not one, but two, full-sized steamboats in the knowledge that at least one would be sacrificed to the arduous filming process that lay ahead.

Wright, who runs Amazon steamboats for tourists, often bumped into the cast and crew in a local German-run restaurant, and warmed to Herzog enough to loan him his chief engineer during filming. "He seemed a good guy, very approachable, not like a lot of directors," he recalls. "Most of his extras were locals. The owner of the restaurant ended up playing the steamboat captain, and the mad ship's cook was a guy from down the road, being himself."

Iquitos was perfect for the establishing scenes of the drama a farewell to Fitzcarraldo's brothel-owning lover (played by Italian actress Claudia Cardinale) and the launch of the boat he named after her. Some believed Herzog should have shot the whole film there. Unfortunately, it lacked one crucial component.

"You've got to go a long way from Iquitos to find a hill," explains Wright.

With the added requirement of two rivers running close enough to drag a boat between them, the new camp was built 2300 miles upstream, in thick rainforest.

It was a location that would have taxed even the most saintly of actors. But Herzog upped the ante by engaging a thespian firebrand whose genius bordered on insanity. Klaus Kinski was infamous in Germany for his one-man stage interpretation of Jesus as a ranting psychopath. He had once almost burned down the theatre after hurling a lit candelabra at a lukewarm audience, and was first known to Herzog as a flatmate who lived stark naked in an attic room carpeted with dead leaves.

Herzog had initially ruled him out as Fitzcarraldo on the basis that he would go "totally bonkers" if trapped in the Amazon. He should have trusted his instinct.

"Every grey hair on my head I call Kinski," said Herzog, who had had famously drawn a gun and threatened to shoot his lead actor if he walked off set during their previous jungle collaboration, Aguirre: The Wrath Of God.

"Klaus was one of the greatest film actors of the century, but he was also a monster and a great pestilence We were like two critical masses that created a dangerous mixture whenever they came into contact with each other."

Arriving on the same plane as Kinski for this intriguing chemistry experiment was Les Blank, a US documentary maker who had obtained permission from Herzog to record the filming process. "I knew if I could make it back in one piece I'd have some great material," recalls Blank, who would later win the British Academy award for the resulting Burden Of Dreams. "But in some ways I'm amazed I came out of it alive."

Initially content to wander around the camp in his Yves Saint Laurent combat fatigues exclaiming on the "eroticism" of the jungle, the German actor grew first restless, then violent. "It was like working with a wild animal," says Blank, who witnessed Kinski physically attacking one of Herzog's deputies.

"Only Herzog seemed able to deal with him he had a way of talking him down, like a horse whisperer."

For hundreds of native Indian extras already wary at being asked to help drag Herzog's steamboat up a muddy slope, the outbursts of the raving white man were incomprehensible and terrifying. One local chief approached the director and offered to have Kinski killed.

Tempting as the offer must have been, Herzog and his team were facing more serious foes. In one of the region's driest summers on record, scavenging Amahuaca tribespeople launched a hit-and-run raid on the film camp. One man was lucky to survive an arrow through his throat, while his wife took three arrows in the stomach, necessitating eight hours of emergency surgery on a kitchen table.

"I assisted by illuminating her abdominal cavity with a torchlight,"

recalled Herzog, "and with my other hand sprayed the clouds of mosquitoes that swarmed around the blood."

Filming was halted while a crowd of furious extras gathered for a revenge attack. Incredibly, Herzog suggested Blank might like to tag along. "I was terrified," recalls the mild-mannered American. "But I didn't want him to know what a coward I was, so I said I would go if he would go." Thankfully, Herzog thought better of the idea by the following morning. "It wouldn't have played very well in the international press." The disastrous run of bad luck intensified. There were two plane crashes in which five people were critically injured, one paralysed and the death of a young highland Indian who drowned after borrowing a canoe without permission. A Peruvian logger bitten by a deadly snake made the dramatic decision to cut off his own foot with a chainsaw to prevent the spread of the venom. And always, as Herzog reeled from one crisis to the next, Kinski would throw impeccably timed tantrums to ensure that he remained the centre of attention.

"I shouldn't make movies any more," says Herzog in Blank's Burden Of Dreams, clearly exhausted and devastated by each new disaster. "I should go to a lunatic asylum I feel even if I get that boat over the mountain, and somehow I finish that film, anyone can congratulate me, but nobody will convince me to be happy about that, not until the end of my days."

Even the boat was going nowhere fast. Dragged little by little up its muddy slope on an enormous block and tackle with nearly a thousand extras and an unreliable bulldozer, the iconic ark reached its summit only to find that drought had almost dried up the water on the other side. A symbol of cinematic folly, perched like Noah's creation, it sat awaiting the next rainy season, inhabited by a family and two pigs.

Herzog at times seemed close to a breakdown. In Burden Of Dreams, he upstaged his own protagonist with the most memorable soliloquy of the entire four-year marathon. "The trees here are in misery," he mutters, Colonel Kurtz-like, at the steaming foliage. "And the birds are in misery I don't think they sing, they just screech in pain So we are cursed with what we are doing here. It's a land that God if he exists has created in anger"

Screen-testing an early edit, Les Blank was surprised to find the audience laughing. "I was baffled," recalls Blank. "I thought it was kind of tragic and sad, but I edited it some more and they still laughed. So after that I played it for the laughter it's basically a tragicomedy."

The tragicomedy verged on farce when filming the scenes in which the steamship is cast off into the rapids by the same Indians who have dragged it over the mountain. Recklessly filming aboard with Kinski and Herzog in a final bid for authenticity, Herzog's three cameramen were flung through the air as the boat swung into a rockface. One suffered concussion, another broke ribs, while the unfortunate Thomas Mauch already missing part of his toe after a piranha attack now had his hand split open in the collision.

With no anaesthetic left after the arrow attack, Herzog recalls how one of the camp's prostitutes (recruited at the suggestion of a Catholic priest to prevent unrest among the loggers) helped muffle Mauch's screams during the ensuing operation by "burying his face between her breasts and telling him how much she loved him."

Twenty-five years later, the old steamship lies rusting somewhere in Iquitos. On the waterfront promenade the Fitzcarraldo bar and restaurant displays her masthead and assorted posters, though few locals can tell you about them.

"Most people round here haven't actually seen the film," explains Paul Wright, munching cheerfully on pan-fried caiman. "It's not really their bag. To be honest I enjoyed the documentary more than the film."

It's a not uncommon verdict. While Fitzcarraldo won Herzog a best director award at Cannes in May 1982, it was perhaps as much for the Herculean feat of making it as for the beautiful but flawed end-product. Burden Of Dreams, on the other hand, picked up the British Academy Award for best documentary and more recently a ranking by veteran film journalist Derek Malcolm among the 100 best films of the whole of the 20th century a list from which Fitzcarraldo is tellingly absent.

Others argue that the two accounts belong together. "I think of them as companion pieces, even parts of the same film in many ways," says film critic Mark Cousins. "But Fitzcarraldo is probably the last film since silent cinema where you're moved by the effort behind making a picture. It's the same reason Victorians went to see the Alps to see the sublime. That's why you feel like applauding at the end. That's its significance, not its content as a work of fiction."

Herzog himself has turned largely to documentary making in recent years. It seems there are enough real-life tragic dreamers like Timothy Treadwell, ill-fated bear-whisperer and subject of his critically acclaimed Grizzly Man (2005) without the need to employ actors to bare their teeth.

The ranting Klaus Kinski father of Natassja perhaps inevitably died of a heart attack in 1991, having alienated almost everybody he knew. A solitary son attended his funeral, while Herzog estranged since filming Cobra Verde in 1987 produced the affectionate if brutally honest documentary tribute entitled My Best Fiend.

A quarter of a century after their most famous collaboration, in an age when a steamboat scaling a hillside would be a doddle for CGI post-production geeks, Fitzcarraldo seems a grand, prematurely ancient work.

"Probably no one will ever need to do again what we did," says Herzog, looking back on the artwork he finally floated on a budget of $6 million and a torrent of incessant stress.

"I am a Conquistador of the Useless."

Log on to www.wernerherzog.com; and www.lesblank.com