David McVicar’s production of Berlioz’s opera Les Troyens at the Royal Opera House last month was notable for several reasons. Firstly, stellar vocal performances from world-class lead singers; secondly, brilliant acting; thirdly, ravishing music; and lastly, a memorable set – including a curious giant horse and human made out of what looked like scrap weapons and tools. With two out of four absent for the eleventh concert in the 2012 Proms season, the prospect of a four-hour-plus performance, truly deserving of the label ‘epic’, was perhaps not ideal on a spectacular summer’s evening. It proved a slow-burner. Stripped down to as bare bones as possible with this work, which tells of the Trojans’ exit from Troy with a relatively straightforward plot compared to Virgil’s convoluted tale, the music itself shone. Meanwhile, the audience were left wondering why the dramatic pulse of the opera took so long to make an appearance.

Berlioz never saw his overture-less opera performed in his lifetime – this is unsurprising considering its logistical challenges and sheer length. It was perhaps a surprise that nothing had been cut from the score tonight. In the staged version, dancers had filled the balletic interludes in the score with some questionable choreography. Without them, the concert felt even longer; but at least here we could dwell on the score rather than working out the purpose of dancers.

The first two acts passed slowly. The only performance to write home about thus far – and what a performance it was – was Anna Caterina Antonacci’s stunning Cassandra. This was the turn of the night for sheer spine-tingling singing value. Antonacci’s rich soprano was suitably angst-ridden and full-bodied, but never reduced itself to wailing.

At this point, all the drama was in the score. The notoriously cavernous acoustic of such a vast arena played into the hands of the sizeable Royal Opera orchestra. They filled the corners of the Royal Albert Hall with Berlioz’s technicolour orchestration, sweeping as it does across so many emotions, compositional styles and influences. What registers are rhythmic motifs and snatches of melody which drive along compelling harmonic arcs. Here is another instance where one wonders what Berlioz would have achieved as a film composer. The imagination and musical breadth in his writing are superb, using every part of the orchestra to best effect.

During Acts I and II it felt odd to have so detailed a libretto. This reminded one of what we were missing in not having a full staging – it would perhaps have been most rewarding not to look at the stage, but to listen to the music while imagining the action as set out in the stage directions. As a minor illustrative point, take the moment when the noble Chorebus tries to persuade his lover Cassandra to cease her doom-laden predictions (always a losing battle) and her insistence that he leave. He pleads: ‘You must listen to me. I clasp your knees!’ At this point, the pair were at least a metre apart, singing eyes front out into the arena – and certainly nowhere near each others’ knees.

Through no fault of the performers, it was sometimes difficult to keep up with the plot in the first two acts. Troy does not burn before our eyes in this version, but its demise begins in the gap between Acts I and II and is then told away from the action by the Ghost of Hector, warriors of the city (including Bryan Hymel’s Aeneas) and ‘distant cries’. It’s when Cassandra, just before she kills herself, gathers with the women of Troy to decide whether to commit suicide or be captured that the act’s most powerful moment arrives. Here the female chorus were magnificent. In fact, the whole chorus were magnificent for the entire performance. They displayed great stamina and sensitivity in conveying vulnerability, grief and excitement in ample measure, losing none of their precision or diction.

Moving on from the varying success of this first segment of the concert, Acts III and IV were where it really kicked off. Eva-Marie Westbroek is surely among the world’s leading operatic sopranos at the moment. The opening of Act III, setting the scene in Dido’s kingdom Carthage, meanders a little, but Westbroek’s singing was energised and her interactions with Hanna Hipp’s Anna were energising to watch. Hymel’s Aeneas also bounced off Westbroek well. The love duet in Act IV was a particularly memorable moment, the pair seeming to fill the hall.

For the final act, the energy just about held out. Whether the audience were still on the ball is another question – there was a distinct outward stream at each interval. Those who did stay, however, could surely not doubt that Pappano at the baton and every musician on stage had given their all, to produce a very solid concert of literally epic proportions – no mean feat.