When Hollywood director Oliver Stone asked Robin Lane Fox to name his price for helping to bring Alexander the Great to the big screen, the Oxford historian had his answer ready.

After a lifetime pursuing Alexander in ancient texts and military histories, he realised that Stone could offer him something he had dreamed of all his life -- the opportunity to ride into battle with history's greatest commander.

"I suppose I should have said squillions of dollars and an option taken out on my book," said Mr Lane Fox, 58.

"But I told him, 'I want to ride in the front 10 of every major cavalry charge involving Alexander and the Mace- donians.'"

British cinema goers will have to wait until January to see his efforts in epic battle scenes filmed in Morocco, and Thailand, where the bare-legged don was pitted against elephants for scenes in the blockbuster Alexander.

He flew to Los Angeles to join the film's stars Colin Farrell, who plays Alexander, and Angelina Jolie, at a private showing of the $226m epic and was reduced to tears.

"I just found it very emotional seeing the leading cavalry charging into battle," he said.

"I am a historian of Alexander -- for me to be able to find out what it is like at the head of his cavalry in his biggest battles is quite extraordinary."

The New College fellow's contribution, however, extended beyond displaying his horsemanship, developed over a lifetime of fox-hunting.

As the author of the biggest selling biography of Alexander the Great, he acted as the film's historical consultant, being called upon to answer questions about everything from why did Alexander wait so long at Tyre in 331BC to how did Greeks wipe their noses. The film's treatment of Alexander's sexuality has upset some Greeks because they say Alexander is depicted as bisexual. But Mr Lane Fox, whose daughter Martha is the celebrated dotcom millionaire, insists that the film is "rooted in history". He said: "In this film Alexander has a sex life, but certainly not a one-way gay or camp one. The issue is admirably treated."

He has just written and published the official guide to the epic, The Making of Alexander and writes of his happy working relationship with Hollywood firebrand Colin Farrell.

He said: "On screen, Colin acted with such force that he even drove his spear through Gary Stretch's body armour and drew blood."

The don was spared the rigours of 17 days military training in a boot camp under the fearsome eye of Vietnam veteran and battle scene specialist Captain Dale Dye.

He joked: "The only two exceptions were eunuchs and Oxford professors."

In the Moroccan desert he fought alongside 1,500 men, which with the use of computers would come to resemble Alexander's army at Gaugamela which numbered 49,000.

In the charges in Thailand, he learned that in a dust cloud horses are as stressed as men.

The Hollywood director was certainly impressed by the Oxford man's contribution.

Mr Stone said, "I'll always remember the day he came to me covered in dust after several charges and exclaimed with a schoolboy's enthusiasm, 'Oliver, you know I've just done the one thing I wanted most of all to do in my entire life...I can never thank you enough."