Composers of the past did not always know their predecessors’ work as we do. Mozart’s musical upbringing being utterly of its time, the music he heard in his formative years was principally that of his older contemporaries rather than of the previous generation. Travelling around Europe with his family as a boy during the 1760s and 1770s he encountered all the fashionable local styles, incorporating them into his own with an ease that has led one writer to characterise him as a 'musical blotting paper'.

By the time he moved from Salzburg to Vienna to begin his freelance life as a composer, pianist and teacher in 1781 he had soaked up elements of the latest Italian operatic and instrumental styles in his operas, symphonies and chamber works, the depth and seriousness of French tragédie lyrique in his first great opera Idomeneo, the conservative Austrian church tradition in his Masses and other sacred pieces, a touch of the state-of-the-art High Classicism of his older compatriot Haydn in his instrumental works, and the melodic grace and elegance of the London-based Germans Carl Friedrich Abel and Johann Christian Bach. Armed with these, and backed by his stupendous natural talent, he entered his mid-20s with a self-confident, wide-ranging and thoroughly modern musical personality.

But the influence that would strike us today as a central one for any Western composer made its impact only late in Mozart’s life. Soon after the move to Vienna he met Baron Gottfried van Swieten, a court official with what at the time would have been a rare and eccentric love of 'ancient music', which in this case meant that of 50 years or so earlier, the era of the High Baroque. Having travelled widely in Europe himself as a diplomat, van Swieten had taken the opportunity to hear and collect music which would then have been virtually unknown in Austria, including works by JS Bach and Handel. Following his visit to London in 1769, in particular, he would have come away in no doubt of the esteem in which Handel was held in his adopted country, and may well also have left carrying copies of some of his works. Whatever the case, he devoted much energy during the 1770s to ordering (via an English contact) as many published Handel scores as he could.

Settled in Vienna from 1777 onwards as Prefect of the Imperial Library, he proceeded to organise weekly chamber concerts in his own home at which his passion for 'old' music could be indulged, and it was here that the gap in Mozart’s appreciation was filled: 'Every Sunday we go to Baron von Suiten [sic]', Mozart wrote to his father in April 1782, 'and there we play nothing but Handel and Bach.' 

It should not be thought that Mozart was previously unaware of Handel; on his own visit to London in 1764-65, only a few years after the great man’s death, he had encountered works of his at court and at the pleasure gardens, and may well have heard some of his oratorios, which were still being regularly performed under the direction of men such as Thomas Arne, John Stanley, and Handel’s former assistant, John Christopher Smith. He also met many other people, musicians and non-musicians alike, who had known Handel personally. 

But it appears that it was only in Vienna, after his meeting with van Swieten, that the power of the Baroque style hit him with its full force. Soon he was borrowing scores, making string quartet arrangements of fugues from the Well-Tempered Clavier (K405) – at that time still unpublished and circulating only among connoisseurs in manuscript copies – and composing exquisite Baroque-style keyboard pieces of his own (rather charmingly, as presents for his new wife, who loved them). 

He also wrote home to his father, asking for copies of fugues (presumably held in the family library) by Handel and Johann Ernst Eberlin, writing again only 10 days later with what today would seem the unremarkable observation that Eberlin’s efforts were 'far too trivial to deserve a place beside Handel and Bach'.

Above all, the realisation of the expressive potential of Baroque music found voice almost immediately in Mozart’s own music, at first in the grandiloquent choruses of the great Mass in C  minor, but also in a four-part fugue, also in C  minor, that he composed for two pianos in 1783, and which five years later he arranged for strings and prefaced with an Adagio much in the style of an overture by Handel (K546). This is no mere exercise in pastiche, but a piece of almost terrifying cumulative power, an acknowledgement of earlier genius that is deeply, almost disturbingly personal.

But a much closer involvement with the music of Handel was still to come. Van Swieten had assembled a group of aristocratic patrons for the purpose of sponsoring performances of rare older choral music, and for their private concerts he invited Mozart to prepare new performing editions of a group of Handel oratorios: Acis and Galatea was the first to receive the treatment in November 1788; Messiah followed in March 1789, and the Ode for St Cecilia’s Day and Alexander’s Feast in July 1790. Doubtless Mozart was glad of the money, but, far from being workaday, the job he carried out on the scores is careful and considered, clearly born out of respect for Handel’s skill and creative personality.

His main objective was to recast Handel’s music – whose original Baroque orchestral line-up of strings, oboes and bassoon and occasional brass and timpani would have seemed a little thin to Classical ears – for an up-to-date ensemble which added flutes, clarinets and horns. He thus brings a warm Viennese glow to the music, but in places Mozart also added his own gloss to events, as for instance in Messiah when he adds a contrapuntal shadow to the stark unison accompaniment of 'The people that walked in darkness', or when he adds his own expressive comments to the already lugubrious 'He sung Darius great and good' in Alexander’s Feast.

Elsewhere there were more purely practical considerations to be taken into account: the art of clarino (or high natural trumpet-playing) needed for 'The trumpet shall sound' was already a lost one in Mozart’s day, so instead he devised a new obbligato part for horn.

It is perhaps only in recent decades that the idea of re-orchestrating Handel has come to need defending; for much of the two centuries following Handel’s death it was almost taken for granted. What is more, Mozart’s arrangements enjoyed considerable prestige during the 19th century following their publication in the early 1800s, withMessiah in particular serving as a starting-point for numerous subsequent editions and re-arrangements, including the one produced in 1902 by Ebenezer Prout and much used by Britain’s choral societies throughout much of the last century.

As for van Swieten, no doubt heartened by his successes in getting Handel’s oratorios performed, he later commissioned through his noble friends (now known as the Gesellschaft der Associierten) two original oratorios by Haydn, The Creation and The Seasons, both of which took the Handelian model forward into the 19th century, where it continued to flourish as a genre, most notably at the hands of Mendelssohn. According to his widow, Mozart himself would have composed oratorios of his own had he lived. Van Swieten it most probably was, too, who introduced Handel’s music to Beethoven around 1800 (perhaps partly in Mozart’s editions); Beethoven later raised Handel above Mozart to stand at the head of his own personal pantheon of great composers.

Antiquarian though he was, van Swieten thus well understood how to give his treasures life beyond that of the museum piece. He also seems to have appreciated not only the value of bringing Handel into Mozart’s life, but also the returns it would bring for both composers’ reputations, as he revealed in a letter to Mozart: 'Anyone who can clothe Handel so solemnly and so tastefully that he pleases modern fashion on the one hand, and on the other shows him in his sublimity, has felt his worth, has understood him, has penetrated the source of his expression, from which he can and will draw with assurance.' Thank goodness the opportunity did not go begging!

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