Not Life and Death but Love and Death are the quintessence of tragedy, as the greatest of Russian novels made plain. We need to know light to know dark, and by some convergence of national history and character, it's always seemed the Russians have the prime claim to the darkest of darks. In Kenneth MacMillan's ballet Anastasia, the story of the youngest daughter of the last of the Tsars, the opening act is one long vista of dazzling sunlight. The Romanovs relax en famille on the deck of the imperial ship, there are girls in white dresses, there is love and laughter, there are some of the most exquisitely carefree dances ever created for the ballet stage. Yet it is more than this spectacle of intense happiness that moves the audience, and that draws it into the drama with such urgency. In a brilliant use of tragic irony, MacMillan uses our pre-knowledge of the ghastly events of 1917 to condition our responses to the ultimate beauties he can devise. And the effect is shattering.

It is hard to believe, after the triumph of Thursday night's opening of the Royal Ballet's new production, that the piece was received badly on its first showing in 1971, leading to 18 years of neglect. MacMillan had added two preceding acts to his original one-act ballet of 1967, which was inspired by the real-life story of an enigmatic German woman claiming to be the Tsar's youngest daughter. Placing the disputed Grand Duchess Anastasia in a mental asylum, he had her recall in flashback her happy childhood, the murders of her family, her escape and subsequent struggle to prove her identity.

The contrast between the opulent first two acts which set the scene before the Bolshevik uprising, and the stark anguish of the last, set in the 1920s, is certainly extreme both in balletic style and in the musical score - the first two are Tchaikovsky's; the last, stringent Martinu.Yet the Romanov acts offer much more than mere documentary information or an opportunity for spectacular ballroom scenes and love duets. They set out the psychological groundplan for MacMillan's complex choreographic code: layer upon layer of gestural meaning that is more akin to the novelist's art than the dramatist's. But in a novel you can read the passage again. In a ballet the images are fleeting and must build in the eye's memory. In no other work I have seen is this more potently achieved.

In a lilting trio for the young duchesses, a repeated hand-on-lip gesture speaks volumes of their charmed existence; in Anastasia's early solos, little groggy jumps of girlish joy capture poignantly her unawareness of adult troubles, let alone the greater griefs to come. And the ghoulish presence of Rasputin which intrudes on the most intimate moments between the Tsar and Tsarina - he sometimes insidiously linking hands with her over her husband's head - are a highly charged metaphor for the corruptibility of the doomed imperial court.

Bob Crowley's new designs are joyfully apt. A grand, shiny ship's funnel surmounted by a giant eagle and a thousand brass rivets ominously smokes throughout the first act, while the most lifelike sea glints enticingly below the deckrail. At Anastasia's coming-of-age party in Act II, huge leaning chandeliers are also the swinging censers of the Orthodox Church, issuing acrid incense - the smell of death - to the back of the auditorium. The violent intrusion of the Bolsheviks while the ball is in full swing, setting fire to the rooftops and unfurling red banners the height of the stage before wading in with their rifle butts, is thankfully brought to a swift conclusion. The gory details are left to the programme notes. The asylum is a miracle of symbolic restraint - all grey and blank but for an iron bed, and apparently seamless grey walls in which apertures suddely open and close like windows on a mind gone dead. Archive film of Bolshevik executions - and of the Tsar's family in what must be among the earliest images on celluloid - give a riveting sense of the historical nearness of it all.

And the performances! As Anastasia at all stages of womanhood, Viviana Durante the immaculate dancer proves also to be Durante the unsurpassable actress. The show is hers. Yet Adam Cooper infuses his supporting role as rescuer and lover with rugged emotional power, and Christopher Saunders and Elizabeth McGorian are superb as the Tsar and Tsarina - proud, in love, painfully aware of the coming day of reckoning yet maintaining dignified propriety to the last. Despite minor alterations overseen by MacMillan's widow, there are still slight lulls in pace in Act II, but the fault here may lie more with the lesser quality of Tchaikovsky - more pomp than circumstance - than with the choreographer's inspiration. But these are feeble quibbles in a production that left the audience still applauding and refusing to leave long after the houselights went up. Here at last is the ballet that triumphantly proves MacMillan's credo: that there is no story worth the telling that can't be told in ballet. The greatest playwright would be hard pressed to match this magnificent work for dramatic clarity and insight.

'Anastasia': ROH, WC2 (0171 304 4000), continues for eight more performances.