Of those three tall poppies, Tantalus, Prometheus and Lucifer - who all had to be cut down by the gods they defied - only Tantalus went on to achieve linguistic immortality. Charged with stealing their ambrosia and passing on their secrets to ordinary mortals, he was condemned by the gods to stand in deep waters which tantalisingly receded whenever he tried to assuage his thirst while overhead a rock hung, ready to fall and annihilate him at some future, unspecified moment.

Tantalus, which Peter Hall has directed in partnership with his son, Edward Hall, begins a British tour which can only be described as a triumph of titanic proportions - as well as the fulfilment of a dream for the Royal Shakespeare Company's director John Barton, who spent 17 years researching and writing the script.

Tantalus tells the story of the Trojan War and includes all the usual suspects - Helen, Clytemnestra, Achilles and Orestes among them - though Tantalus himself fails to makes an appearance. Instead, a huge rock creaks overhead as a terrible reminder to the characters - and to us - that, in Barton's words, "death is inevitable, but doom is postponed".

Tantalus consists of nine plays, each of about an hour's duration which can be seen three at a time on consecutive evenings or all on one day, starting in the morning and ending in the evening - with two comfort breaks in a performance that lasts nearly 10 hours. The first cycle of three plays deals with the outbreak of the Trojan War, the second with the war itself and the last with the homecomings of the participants.

The actors, appearing in all three cycles, play anything up to three parts each, some metamorphosing from bikini babes on an Aegean beach to a classic Greek chorus with attendant fallen statues.

Both Hall and Barton have already tackled the myths. In 1980, at London's Barbican Theatre, John Barton put on The Greeks, of which Tantalus is an extension. In the same year, Peter Hall directed the mesmerising Oresteia at the Olivier, in which the masked, all-male cast held the stage for five hours, their gender betrayed only by their sinewy arms and large hands - always a giveaway in any drag act.

This is the first time, however, that the two directors, colleagues as well as old friends (they were at Cambridge together) have collaborated on such a huge undertaking. So huge has it been, in fact, that it could only be mounted with financial support from Colorado businessman and lawyer Donald Seawell, a board member of the Denver Centre for the Performing Arts, which, with its nine auditoria and resident ballet, orchestra and theatre companies, is America's biggest. Seawell, on the board also of the Royal Shakespeare Company, added £6.5 million to the British Arts Council's touring grant of £460,000. Without the dollar input, it would simply not have been possible to mount the production which includes an Anglo-American cast of 27, Greece's foremost theatrical set designer, Dionysis Fotopoulos, the Broadway choreographer Donald McKayle, a Japanese lighting team, and Irish composer Mick Sands. The play was six months in production in Denver before finally opening there on December 2nd last year.

With so much invested in terms of money, time and reputations, it would be foolish to expect such an enterprise to have been trouble-free. One American actor pulled out, disputing the appropriateness of wearing masks. Associate director, Co Down man Mick Gordon left the production in the early stages and still doesn't want to talk about it. But, most shattering of all, John Barton, progenitor of the whole show, had a falling out with Peter Hall and left for London. He dissociated himself from the production and chose not to attend the opening night in Denver - although he did turn up the following week.

The problem arose from the length of the play. Barton delivered play scripts totalling 14 hours of time which was, in Hall's view, about four hours too long. Having done so much work on it, however, Barton was not prepared to tolerate any cuts.

Which is why, on his departure, Hall brought in Dublin playwright Colin Teevan, currently head of drama at Queen's University, Belfast, with whom he had previously worked.

"Originally," says Teevan, "I was brought over to observe the play and possibly to write the screenplay of it. Then, as things turned out, I was brought back as associate director and asked to do a massive overhaul. It was a difficult task. I was given 600 pages comprising 20 years of someone else's labour and I had to find how best to present John's work. His phrasing, for instance, is English and mine is Irish." Hall was a hard taskmaster. "He doesn't take the foot off. We worked nine to seven, six days a week," says Teevan, who, for the duration, installed his family in one of Denver Arts Centre's 48 company apartments, which come with gym and pool. The cuts were eventually made and the new writing done and now the programme notes read: "Additional material by Colin Teevan." Two aspects of the production were particularly challenging: accents and the masks.

"My feeling initially," says Teevan, "was for people to do it in their own accents but with an Anglo-American cast, this would have meant a husband and wife or mother and son speaking in two different accents. The Americans don't worry about something like this - accents are a British obsession - but in the end it was decided some sort of standardised compromise should be reached."

Of course, it's anybody's guess how the Greeks and Trojans spoke all of 3,000 years ago, so doubtless the Americans are right not to be unduly worried about accents.

The business of whether or not to use masks was also hotly discussed. Barton didn't want masks used and Hall did. "British actors," says Teevan, "are used to the verse-speaking tradition, more than Americans. That was one thing. Then, Greek dialogue is not characterised and although John didn't want masks used, his writing wasn't characterised either so the use of masks helped to portray the different parts. What we did was build the masks into the story so that they became an integral part of it. In the fourth play, for instance, we see the chorus put on their masks and in another scene, two lovers actually take them off in order to declare their love."

And while the eponymous character never makes an appearance, the Trojan horse is larger than life. "It's bigger than the theatre itself," says Teevan and, given the nature of the drama, that's exactly how it should be.

Tantalus began its UK tour in Salford on Saturday, where it will run until February 3rd; it then tours to Nottingham, Milton Keynes, Newcastle and Norwich before a four-week run at the Barbican from May 2nd to May 19th. u20 per play to u80 for the one-day show. The RSC information line: 0044 1789403440 and www.rsc.org.uk

The original text of John Barton's Tantalus is published by Oberon Books at £9.99