Juliet as portrayed by a force of nature

Romeo and Juliet
Royal Opera House, London WC2

When Kenneth MacMillan choreographed Romeo and Juliet for the Royal Ballet in 1965, he created the most fiercely coveted ballerina role of them all. The canon isn't short of tragic heroines - Giselle, Odette in Swan Lake, Tatiana in Onegin - but it's the beautiful, doomed Juliet every ballerina dreams of dancing.

One of MacMillan's great skills was making dancers look fabulous without imposing severe demands on them, so the role isn't technically daunting. Dramatically, though, it's a huge challenge. Romeo can express himself through action, but Juliet is condemned to a life of being, not doing. To counter this, MacMillan has given her choreography extraordinary transparency, with every whisper of her feelings revealed through dance.

It's in the hope of emulating the great Juliets - Margot Fonteyn, Lynn Seymour, Tamara Rojo - that many of the world's best young dancers set their sights on the Royal Ballet. The role was on Marianela Nuñez's mind when, aged 15, she flew from Buenos Aires to Los Angeles to try and wangle an audition with the Royal, then on tour there. They took her, but it's taken Nuñez 11 years and a string of glittering successes in other roles to win the gold-and-white Capulet ballgown.

Although a prodigious technician, Nuñez is essentially an instinctive dancer, illuminated from within, rather than reflective of events around her. Her Act 1 is especially lustrous, with her delicately aristocratic bearing counterpointed by a reckless hunger for experience. We see this in her immediate delight at Paris (David Pickering) and her equally immediate forgetting of him, in the flirtatious sparkle of her ballroom dance and, above all, in the balcony scene.

There's a key moment in the pas de deux when she runs to Romeo (Thiago Soares), whips off a fast multiple pirouette and then extends her leg into a smooth, waist-high circling of her body. Every Juliet does this slightly differently, but with Nuñez, the segue from the racing blur of the pirouette into the rapturous precision of the rond de jambe is heartstopping. This is when the maidenly evasions end. This is when maybe becomes yes.

Sarah Lamb, who joined the Royal four years ago from the Boston Ballet, is this season's other new Juliet. Lamb is a more detached performer than Nuñez and her Juliet more questioning of her situation. Her first reaction to Romeo (Viacheslav Samodurov) is curiosity verging on suspicion, and she approaches their first dance together as if awed by her own daring. Where Nuñez makes light of the rivalry between the two families, Lamb knows exactly how dangerous a game she's playing. But the softening of her initially rather crystalline dancing and the growing amplitude of her phrasing tell us that she is already half in love and in the balcony pas de deux, she signals her surrender to destiny not with the rond de jambe but the plunging, fatalistic arabesque which follows it.

Their Romeos offer a similar contrast. Samodurov, if technically underpowered, is an affectingly heartbroken lover, while Soares's volatile street fighter travels from incredulity at his capture of the luminescent Nuñez to a ragged, savage cursing of fate. Given his saturnine bearing and the aura of darkness that he trails, it would be fascinating to see Soares as another MacMillan antihero, Crown Prince Rudolf in Mayerling.