The cobbled streets of Pavia twist and turn and lead to various grand Roman-Lombardesque churches that lie sprinkled around the town. These attest to those days in which the town was the seat of the Lombard monarchs, as do the clusters of medieval towers that punctuate a skyline dominated by the Cathedral's vast dome. Evening wanders inevitably lead to the Strada Nuova, a broad, cafe-lined vista that leads down to the River Ticino, at the top of which sits the Teatro Fraschini, one of Italy's oldest theatres. This was the venue for Ton Koopman's much-awaited recital of Bach's Partitas for Keyboard.

The Partitas are a compendium of Bach's styles for harpsichord in which thematic material is first presented in an opening movement and then distilled through successive sarabandes, gigues and fantasies. The works were published together under the title Clavier-Übung I (“keyboard exercise”), the first page of which reads “composed for music lovers, to refresh their spirits”. Such information is initially misleading; far from light refreshment, these works are widely regarded as Bach's most difficult for keyboard. As Koopman glittered through the aristocratic dances of Partita no. 3, his posture straight and noble, head occasionally dipping at moments of discord, he played with a clarity of style that brought out the contrasts between the movements and displayed their structural complexity.

Koopman's fine playing was at its most enchanting in Partita no. 4, where tiny moments of elasticity produced waves of energy that ebbed and flowed. The opening Ouvertüre was all grand dotted rhythms and silky legato, and this opened into a horizon of whirling semiquavers in which the texture gradually thickened in the middle of the keyboard and the momentum built. The melancholy Sarabande that followed featured a meandering walking bass that interwove with arabesques above to create deliciously piquant dissonances. In one particularly visual moment, a snaking gesture passed down from the right hand to the left, and rushed to a heady peak, before gliding back down to earth in circling triplets. In this world of baroque ornaments, wandering eyes could freely train the rococo-swirled proscenium or become lost in the copiously folded robe of Apollo who gazed down from the painted ceiling.

Koopman is perhaps better known for his conducting of Bach's choral works nowadays than for his playing, though he initially trained as a harpsichordist under the guidance of legendary player and fellow Dutchman, Gustav Leonhardt. The latter was amongst the original pioneers of the “historically informed performance” movement whose proponents scoured baroque treatises and performed on historical instruments. When Koopman joined this revolution, to use his own term, it was still very much an underground phenomenon where long-haired musicians played to audiences in abandoned churches. Much of the music world reacted coldly to these groups because, Koopman has suggested, their members were deemed to be abundant in vision but lacking in musical skill.

Such criticisms are now rarely heard, and Koopman showed why. He is part of a generation of virtuoso interpreters who command respect. Koopman's own talent could not have been more evident than in the fiendish scales of the Toccata of Partita no. 6, where his hands skated up and down the keyboard with fluid dexterity. But most of all, his performance demonstrated some of the harpsichord's advantages over the piano in this repertoire. The dynamic inflexibility on this instrument is perhaps a source of its strength, with all voices inevitably awarded equal aural value. The result was intricate yet perfectly lucid tapestry that at times was utterly mesmerising.

In addition to his technical skill, Koopman possesses a zest that shone through in the freshness of his interpretations. Here, we were reminded that early music is perhaps less a reactionary attempt to place music within the stringent confines of what is deemed “correct”, and more an inquisitive, excited spirit of discovery.

As early music's stuffy image has begun to evaporate, its way of thinking has percolated into new areas. Koopman recently completed a three-year residency with The Cleveland Orchestra, whilst early music groups now tackle repertoire traditionally outside of their prerogative (as with last years Prom's concert of Brahms with The Orchestra of the Age of Enlightenment under Marin Alsop). The barrier between early music and other is perhaps more porous than ever, and Koopman has surely been a key architect in this process. 

His efforts were certainly appreciated tonight, and as he concluded Partita no. 6 with an arpeggiated flourish, right hand recoiling dramatically, the audience demanded more. Koopman provided an elegantly conveyed movement from one Bach's French Suites, and when even this wasn't enough, he turned to Purcell's Ground in C minor in a rendition that summed up his style. Haunting rotations of unsettling syncopation were treated with silvery legato, liquid embellishments and choice moments of rubato that brought the music to life.