On the evening of October 9 1963 part of a mountain collapsed into an artificial lake in north-east Italy. The resulting tidal wave leapt over what was then the world's highest dam and swept more than 2,000 people to their death in the Vajont valley below.

Now the events leading up to the tragedy are the subject of a film, Vajont, which will be given an exceptional premier today, projected on to the dam wall while an expected audience of 1,300 - mainly survivors of the disaster and their relatives - use the remains of the landslide site as an amphitheatre.

The director, Renzo Martinelli, has chosen the audience and location to honour those survivors whose recollections of the tragedy form the basis of the screenplay.

"I promised these people that as soon as the film was finished I would bring it here and show it for them on the dam wall," he said.

Two days after the catastrophe, Dino Buzzati wrote in the Corriere della Sera: "A stone has fallen into a glassful of water and the water has spilled on to the tablecloth. That's all.

"Only the glass was hundreds of metres tall and the stone was as big as a mountain and below, on the tablecloth, were thousands of defenceless people."

The stone was actually a huge chunk of rock which fell into the reservoir at a speed of 60mph after slipping from the flank of Mount Toc.

It set up a wave 250 metres high which swept over the dam, leaving it miraculously intact, but destroying towns and villages in its path below.

It was not a natural disaster, however.

"People remember it as a natural catastrophe, but it was the work of men - of men who ought to have taken action but didn't," Martinelli said.

"When the dam was 100 metres high, people realised that the mountain was dangerous. But too much money had been invested and a systematic cover-up began."

Martinelli, who also directed Porzus, a film about a second world war partisan atrocity, said he hoped Vajont would serve to forge a social conscience that would make such disasters impossible in future.

The film stars Michel Serrault, Daniel Auteuil and Laura Morante, and the tenor Andrea Bocelli sings on the soundtrack.

"I hope the film will make people reflect on the dangers involved when private commercial interests combine with political power to cause disasters," Martinelli said.

Thirty-eight years on, the film has a particular resonance in the Italy of Silvio Berlusconi, who has managed to meld political and financial power as never before.

"My aim was to show that we have the talents and resources in Italy to make important films. We will see how the market responds in the coming months," Martinelli said.