The Elgin Marbles in the British Museum are marvellous - but they're a bit, well, colourless , aren't they?

That isn't how it was for the ancient Greeks. The sculptures were painted in vivid colour. High up on the sides of the Parthenon temple in Athens, they had to be.

Now a new film on permanent show in the room next to the Marbles adds the colour - and the fear and the violence.

"When we started to apply the colour it brought a lot of the emotion to life," says Dyfri Williams, Keeper of Greek and Roman Antiquities at the British Museum.

The film reconstructs one of the metopes - the 92 carved fight scenes that ran around the outside wall - using computer technology.

"What you probably hadn't been able to see" in the scene of a centaur hitting a youth with a pot has finally come alive, says Mr Williams.

"The madness of the centaur comes out and the terror of the youth comes out.

"We hope to put that little film into our internet site - the message about colour on the sculpture is so important; it changes people's perception so much that we should have it there."

The subject of the film, south metope no. 4, mirrors the troubles that all the Parthenon sculptures have gone through.

Most of the metopes were defaced by Christians from the 6th Century AD on, when the Parthenon was turned into a church. Those on the south side, depicting a battle between centaurs and humans, escaped - presumably they were thought to convey some suitable Christian message.

But the Parthenon was damaged catastrophically in 1687 when a Venetian army shelled the Acropolis and the Parthenon blew up - the Turkish garrison was using it as a powder magazine.

From that time on the temple was a ruin, and fragments were taken by souvenir hunters, ending up in some 10 European countries, or lost altogether.

Moritz Hartmann, a Danish officer in the Venetian navy, bought the two heads from south metope 4 in a street in Athens in 1688 and they are now in the Danish National Museum.

The rest of south metope 4 was removed from the Parthenon by Lord Elgin's agents in 1802 and - with 14 other metopes and many other Parthenon sculptures - acquired by the British Museum in 1816.

The Greek authorities and campaigners in Britain and elsewhere continue to call for their return to Athens to be reunited with other Parthenon sculptures there.

But the British Museum points out that about 50% of the sculptures are lost forever and the damaged remnants which are left are divided, not just between London and Athens but a handful of other European museums too.

"It is no longer possible to recreate them in any real sense," says the BM. "It must be done 'virtually'."

Lost details

The restored metope is part of this process. The project began with three-dimensional laser scanning of the metope in the BM, and of casts of the two Copenhagen heads, by the National Museums Conservation centre in Liverpool and fitting the images together.

More can be added from a drawing done by the Frenchman Jacques Carrey in 1674. But still a lot of details are entirely lost.

Dyfri Williams's department developed a story board for the film, which Mark Timson of the British Museum's New Media Unit translated into a series of computer-generated models.

Drawings of the missing pieces were developed based on other metopes in the museum.

Fixing-holes in the sculptures show that metal pieces were once included - for this metope, a headband and sword for the boy were added.

The 3-D scanning enabled some things about the carving to be understood which had been a mystery before, says Mri Williams.

Since the scanning, some ridges of the youth's thigh are now thought to mark the folds of his cloak. The museum now thinks the cloak was finished off in plaster, probably after some accident in the carving of the marble.

"This is quite amazing, what you can see with the scan," says Mr Williams.

"You go up and round - and we hadn't noticed that bit about the drapery on top of the thigh beforehand; we knew that there was a roughened patch though it had never really been explained."

And then, the colour. Few traces remain of paint on ancient sculpture, and those that have survived have often changed colour over the centuries. So the British Museum's film shows alternative colour schemes.

But it favours a white background and blue surround, matching the colour scheme found on tombs unearthed in Macedonia.

Accessible to all

"I think that real progress can be made in understanding the fragments scattered all over the world. We can, with the aid of this project, make a lot of progress on that," says Mr Williams.

The British Museum has said the ultimate aim should be to create a "multi-level, interactive educational resource accessible to all" on the internet and elsewhere.

That is still the aim, says Mr Williams, but "it's a matter of assembling the finances for it and the resources to do it - the British Museum has many different things it tries to do."

"This has got to be a collaborative process; it's got to be a sharing of our knowledge.

The Greeks have to be involved, we have to be involved, the Germans have to be involved, the Danes, the French, the Italians - because it involves everybody. Such special sculpture's for everyone."