Ballet is an art whose past is fragile, relying on memory rather than a secure text. Stagings had no proper choreographic scores until the mid-20th century, and dance was handed down from performer to performer with all the inaccuracies that implies. The reclaiming of a balletic history has at times seemed like the reconstruction of a dinosaur skeleton from a single bone, and as unlikely of success. Yet latterly in Russia, at the Mariinsky and Bolshoi Theatres, there has been a quest to explore a heritage by restoring celebrated productions.

Now, in Moscow, Le Corsaire has been restaged. The keys to this and similar acts of dance-piety are the notations, in Stepanov script, of the ballets given at the Mariinsky Theatre as the 19th century ended, which the régisseur Nikolai Sergueyev abstracted from the theatre's archives when he fled Russia in 1918. From these scripts stem most of the classics as we know them in the west: Ninette de Valois acquired our Royal Ballet's versions from Sergueyev in the 1930s. These "ledgers" (de Valois' phrase) record, in varying stages of completeness, both steps and production detail, and are now held in Harvard's great Theatre Collection. Deciphering them, adapting them to the style of today's dancers, is a task only for the brave and those rich in resources. Nowhere better, then, than Russia, where the balletic past is honoured.