Norma, Vincenzo Bellini's 1831 opera, is set in the midst of historical events that will be somewhat obscure to many of us. The drama reimagines the conflict between the Gauls and their Roman occupiers 50 years before the birth of Christ.

However, this is no highbrow version of the famous Asterix And Obelix cartoons by Rene Goscinny and Albert Uderzo. Moshe Leiser and Patrice Caurier, co-directors of this Salzburg Festival production (which premiered in the Austrian city three years ago), have relocated the piece to Second World War France, with the rebellious Gauls as members of the French Resistance and the conquering Romans as German Nazis.

The devoutly pagan Gauls' "sacred grove" is represented by a cavernous schoolroom, which doubles as a Resistance hideout. Norma, the titular druid priestess, is transformed into a patriotic, anti-fascist leader; a secular, 20th-century Joan of Arc, if you will.

The hated Roman proconsul, Pollione (who is, secretly, Norma's former lover and father to her children), becomes a senior Nazi officer. In Bellini's original, Pollione has a taste for Gaulish priestesses; he dumps Norma for Adalgisa, a younger druid. Here he is a fascist Casanova, able, it seems, to bed any female Resistance fighter who should take his fancy.

This may all seem like a considerable mental leap. However, if one is prepared to suspend one's disbelief, this re-envisioning of the opera is every bit as valid as the Royal Shakespeare Company representing Coriolanus as a Napoleonic despot or Macbeth as a modern day Balkan warlord.

Ultimately, Leiser and Caurier, who have been working together for more than 30 years, rest their relocation, quite plausibly, on the story's themes of occupation, resistance, betrayal and, ultimately, fealty to fundamental human instincts. Sex and love, suggests Bellini (or, more accurately, Alexandre Soumet, upon whose tale the opera is based), can lead us to transgress our most deeply held beliefs and principles. That, it need hardly be said, is a universal theme.

The directors and their designers, Christian Fenouillat (sets), Christophe Forey (lights) and Agostino Cavalca (costumes), have done a masterful job of reflecting Bellini's music in their staging. Fenouillat's grand schoolroom, which is filled with the paraphernalia of the Resistance, is the perfect location for the splendid, swirling orchestration that accompanies the outraged demands for vengeance of the French partisans (played superbly by the Swiss Radio and Television Chorus).

By the simple device of bringing down a partition, the back of the schoolroom is transformed into Norma's modest apartment. As Forey's lighting throws premonitory shadows around the set, the intimacy and foreboding is the very mirror of the music, as the desperate Norma, like a latter day Medea, contemplates the unthinkable.

All of which, concept, direction, design, chorus, requires a fine orchestra (which we have here, under the baton of Gianluca Capuano) and excellent soloists. John Osborn, a tenor from the United States, and Rebeca Olvera, a Mexican soprano, give soaring performances as Pollione and Adalgisa respectively.

However, for many, the primary reason for attending this production is to hear Cecilia Bartoli, the internationally acclaimed, Italian mezzo-soprano, sing the title role. Without question, her performance is worth the (in many cases not inconsiderable) ticket price on its own.

Her singing of Norma's great aria Casta Diva, which was popularised in the 20th century by Maria Callas, among others, is a thing of profound beauty. As Bartoli understands, seemingly instinctively, vocal range and power (both of which she has in abundance) count for little without feeling. She sings this plea for peace and patience with a shuddering emotional depth that would pacify the rashest of warriors.

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