Superstar castrati Farinelli and Caffarelli sang at the première of Johann Adolf Hasse’s Siroe. What incredible feats of song ­the Bologna audience must have witnessed! A leading opera composer of his time, Hasse was forgotten after Gluck revolutionised the art form, ditching the ornateness and formulaic structure of Italian opera in favour of simplicity and dramatic veracity. Thanks to the ongoing excavation of Hasse’s works, we continue to rediscover how they hold their own against those by Handel, his most valued fellow exponent of the galant style, with its focus on emotional expression and tuneful elegance.

In 1763, thirty years after Bologna, Hasse put on a heavily revised version of Siroe in Dresden. This time he was more faithful to Metastasio’s original libretto, resetting practically all the recitatives and rewriting fourteen of the arias. This version was used for the Dutch première of Siroe, with abridged recitatives and two arias borrowed from other operas, a common practice in the eighteenth century, one by Hasse himself and one by Carl Heinrich Graun. The passionate and accomplished Armonia Atenea and a cast of baffling virtuosity demonstrated Hasse’s dramatically vivid scoring of the dialogues and asides, the dazzling beauty of his arias, and the depth of expression he achieves with means such as alternating instrumental colours. Although it does not lack stock Baroque characters and situations, Metastasio’s text retains its timeless refinement and his character-driven plot unfolds coherently.

Siroe is the historical Persian prince Sheroe, heir to Khosrow II (Cosroe in the opera). His father imprisoned him to pave the way for his half-brother Mardanshah, son of his favourite wife, to ascend the throne. After much dynastic strife, Sheroe assumed power in the year 628 as Kavadh II, whereupon he promptly had his father and all his brothers and half-brothers executed – he need not have bothered because he died only six months later. The operatic Siroe is not even remotely as bloody: he is principled, peace-loving and loyal to a fault. Although his father Cosroe is willing to believe the smear campaign against him, he refuses to defend himself. His brother Medarse is an oleaginous intrigant, but Siroe forgives him and everyone else in the end, after Cosroe abdicates in his favour. No harem wives in Metastasio, but a piece of work called Loadice, who is Cosroe’s mistress, but is in amorous pursuit of his beleaguered first-born. Siroe is in love with Emira, daughter of an Indian ruler who was killed by Cosroe. She has come to the Persian court to avenge her father, naturally disguised as a man called Idaspe. Divided loyalties torture Emira, and Siroe is also tugged in all directions by love, politics and filial duty. His only friend is Arasse, an army general. “Everyone at court speaks in riddles”, observes Medarse, and the scheming and dissembling result in plenty of emotional crises to be worked through during agitated arie di caccia (arias with horn accompaniment) and anguished cantilenas of extreme loveliness.

This cast and ensemble are used to performing this work together and they appeared comfortable with both score and characters. Armonia Atenea boasted heart-meltingly mellow violins and the tonal palette set by flutes, oboes and horns was in painterly hands. George Petrou conducted with dynamism and all of his choices made perfect sense. Changes of tempo felt organic to poetic expression. Dressed in matching emerald green jackets, countertenor Max Emanuel Cenčić, and mezzo-soprano Mary-Ellen Nesi waged sibling warfare with spiralling vocal fireworks. As the scheming Medarse, Ms Nesi plied her plum-pink mezzo like a sharp dagger, piercing the air with bright top notes. Mr Cenčić’s voice contains a wealth of colour and, excitingly, gains volume and sparkle as it climbs upwards–a complex, noble sound to go with the complex, princely title role.

Tenor Juan Sancho was a theatrically charged King Cosroe, showing vocal daring that was at times post-Baroque. Cosroe gets what is arguably the most dramatically powerful number, the remorse aria “Gelido in ogni vena” (I feel the blood run cold in my veins), which Mr Sancho dispatched with chilling desperation. As Emira, mezzo-soprano Roxana Constantinescu scorched with hatred towards the king, and with satisfying richness in the aria “Che furia, che mostro” (What fury, what a monster), whose range dovetailed neatly with the freest part of her voice. Dilyara Idrisova displayed a willowy soprano in the trouser role of Arasse. Like Mr Cenčić, Julia Lezhneva has a voice with direct star presence. Her angel-faced Laodice dropped her poison and threw her tantrums with a lustrous middle register. At the extreme top, her soprano tends to whiten, but this is a tiny niggle in view of the frightening accuracy and brilliance of her runs. She warbled her way through Hasse’s (and Graun’s) endless curls and twists as blithely as a bird splashing water at its bath–supremely thrilling.