Some 40 years before Mozart turned La clemenza di Tito into what he dubbed a ‘true opera’, Gluck set Metastasio’s idealised take on Roman history more or less unaltered for Naples. With Orfeo still a decade away, the ‘beautiful simplicity’ and stark theatrical immediacy of Gluck’s great reform operas are barely glimpsed in the first half of the opera. Caffarelli, the tantrum-prone star castrato who took the role of Sesto, and the prima donna Caterina Visconti, as Vitellia, demanded, and got, a succession of arias fashioned above all to display their vocal prowess – just the kind of thing Gluck and Calzabigi would later purge from opera.

Structurally this is opera seria at its most formal, with arias – many in jaunty minuet rhythm – interleaved with reams of recitative, and ne’er an ensemble in view until the perfunctory final coro. As the dramatic temperature rises, though, the invention becomes more individual and economical, with hints of Gluckian glories to come. There are, inter alia, powerful accompanied recitatives for Sesto and Tito, a magnificent minor-key aria for the guilt-ridden Vitellia, an affecting plea for mercy from Sesto’s friend Annio and – the plum of the whole opera – Sesto’s ‘Se mai senti’, with its poignant oboe solo and pulsing, syncopated ostinato. Never one to waste a good idea, Gluck would recycle this haunting aria for Iphigénie en Tauride.

Although individual arias have been recorded by Bartoli, Kožená and others, this is the opera’s premiere recording. As in Naples in 1752, the casting of the three principal roles of Tito – who dominates more than he does in Mozart’s opera – Vitellia and Sesto is crucial. Rainer Trost’s baritonal tenor is grittier than a decade ago, though he remains a fine Classical stylist and catches both the Emperor’s dignity and, in the seething aria ‘Tu infedel’, his agony as he confronts his betrayal by Sesto. Laura Aikin, fearless in attack, dazzling in coloratura, brings vocal glamour and fiery temperament to Vitellia’s music, though even she sounds a mite flustered by the precipitate tempo in the aria that closes Act 2. Raffaella Milanesi’s success, as Sesto, is more mixed. She sings with passionate feeling and uses her words more expressively than anyone. But her tone can become shrill in alt, while in ‘Se mai senti’ her emotive sighs and swells become counterproductive.

Among the lesser roles, Valer Sabadus impresses with his rich, sensuous countertenor, reminiscent of Jochen Kowalski. Publio’s two arias – both dramatically redundant – lie uncomfortably high for Flavio Ferri-Benedetti. Arantza Ezenarro, as Servilia, also has moments of shrillness, though she is touching and tender in her avowal of love to Annio, and properly anguished in her final plea to Vitellia, where Gluck’s hectic, angular music contrasts startlingly with the sublime minuet at the same point in Mozart’s opera. With his responsive period band (fast numbers have a crackling, punchy energy), Werner Ehrhardt paces the opera convincingly, while the singers and the inventive continuo (lute and harpsichord) ensure that the potentially tedious recitatives never flag. In slower numbers, not least ‘Se mai senti’, I wanted more subtlety and more expressive shaping of the bass line. But these are relatively minor quibbles. While only the most partisan would claim La clemenza di Tito as an unjustly neglected masterpiece, its second and third acts contain some inspired arias. Anyone curious about pre-Orfeo Gluck should find plenty to enjoy in both the music and the skilled, carefully prepared performance.