The Bolshoi Ballet dances Spartacus with huge, devoted seriousness. Yuri Grigorovich's 1968 ballet is a Soviet account of a Roman slave uprising: heroic gladiators vs decadent patricians, all in big, simple outlines. Khachaturian's score has brassy fanfares, swooping harps and improbable Latin rhythms. The dancers dive into Grigorovich's leaps and spins without a backward glance.

Grigorovich tells his story through four principal characters. Spartacus leads the gladiators' revolt, sustained by the love of Phrygia. The Roman legions are led by the wicked Crassus, supported by the treacherous courtesan Aegina. Women have high leg extensions, men have huge jumps, duets have one-handed lifts.

The current Bolshoi cast have the technical resources for these roles, but they're emotionally underpowered. When Spartacus agrees to lead the revolt, he turns to Phrygia for support. At the end of their duet, Spartacus leaves the stage with Phrygia in his arms and the red cloak of leadership over his shoulder. It's a slow, weighted walk, a conclusion reached. With Dmitri Belogolovtsev as Spartacus, the exit has no force: he just walks off.

Belogolovtsev approaches the role seriously, and the jumps and turns are all there. But the gestures need more authority. It's the same with his co-stars. Many solos stop abruptly, with steps in place but the dramatic point still to be made. Anna Antonicheva, as Phrygia, affects a smiling-through-tears face, but she doesn't add human depth to Grigorovich's melodrama.

The wicked Romans do rather better. As the Roman general Crassus, Vladimir Neporozhny lacks a sense of danger, but he has bounding jumps and a certain overbred petulance. Grigorovich and Khachaturian give us bossa-nova Romans, patricians mincing from side to side while the orchestra shakes its maracas.

Galina Stepanenko, the treacherous Aegina, is a strong, rather hard dancer. She throws too many gestures away in the private "monologue" solos, but she has huge fun with the public orgies.

After corrupting the slave army with wine and whores, Aegina does a pole-dance in triumph. The pole is a pagan fertility symbol, complete with purple flowers on top, and she plunges it gleefully between her thighs, flicking her legs in showgirl kicks. Khachaturian, reliably tacky, throws in some bump-and-grind trumpet-playing.

This was the first time I'd seen Spartacus in the theatre, and I was amazed by how strong it is live. These principals can't match the power of earlier performances - film of Vassiliev and Mukhamedov is astounding - but there's still the exuberant dedication of the Bolshoi corps.

They dance gladiators, slaves, courtesans and the Roman army with even-handed fervour. And they look wonderful. The men jump with tremendous vigour. The women droop gracefully as slaves. Throughout, there's a unison quality of movement, a shared conviction. In the second act, the working people of Rome join the gladiators' revolt. A few minor shepherds wait at the very edge of the stage, almost in the wings. They're barely visible, but they go right on dancing.