Even in the 18th century there were already festivals in Salzburg: whenever students from the town's ancient university assembled in high summer in order to talce their leave of the reigning prince-archbishop and their alma mater, the whole of Salzburg would turn out to watch - not only was the procession of students an attractive sight in itself, but the event featured magnificent music known as Finalmusik. During the summer of 1779 Mozart wrote his last and greatest Finalmusik in the form of the Serenade in D maior K 320, also known as his "Post Horn Serenade" because the penultimate movement includes a corna di posta. Normally post horns were banned when post coaches drove through Salzburg, with the result that listeners must have been all the more surprised when in the second Trio in the second Menuetto the postilion suddenly struck up his fanfare. This was a musical symbol of farewell, reminding the students that it was time ta leave on that August evening in 1779.
For Nikolaus Harnoncourt this passage is not the only valedictory music in the "Post Horn Serenade": "The whole work speaks of leave-taking," he explains. "For many students, this was not just the start of their summer holidays but also the end of their period of study in Salzburg." Even the slow introduction, an Adagio maestoso, creates an unusually serious and emotionally charged impression. It is repeated after the Allegro's long development section, acquiring particular weight in consequence. In the Allegro con spirito impatient syncopations and powerful march rhythms suggest a time of new departures: the whole of Salzburg seems to be on the move, as indeed it was when this serenade received its festive first performance. The second subject seems almost theatrical, the insistently repeated dotted motif in the basses implacably urging the students to leave, while the first violins detain them with a vaguely lachrymose melody. The oboes add their voices with a series of anguished suspensions. Nikolaus Harnoncourt imagines a student saying goodbye to the family that had provided him with board and lodging: "These were friendships that grew up over the years." Once the students had all left, Salzburg was as empty as it is nowadays at the end of the Salzburg festival.
Rarely did Mozart write more magnificent music than in the grandiose opening movement of the "Post Horn Serenade". The farewell scene that we have just described is followed by a double crescendo built up over the motif in the basses and culminating in a veritable song of triumph for the entire orchestra. Clearly Mozart still had in his mind's ear the sort of sounds that he had heard in Mannheim and Paris, where in 1778 he had been able to hear Europe's finest orchestras, bodies of players whose perfection the conservative Salzburgers could only dream about. He now proceeded to import much of what he had heard there into his native Salzburg. At the same time, however, the musical splendours of K 320 reflect the circumstances of its first performance. To the strains of a march the students went first to Schloss Mirabell in order to pay their respects to the prince-archbishop. The Finalmusik was then performed in the palace courtyard, before the court musicians and students made their way back to the university over the River Salzach. During this time they were again accompanied by the march. The whole of the Finalmusik was repeated outside Fischer von Erlach's Collegiate Church. "I know this square very well," says Nikolaus Harnoncourt. "It has outstanding acoustics. You can hear every detail." Mozart clearly wrote his "Post Horn Serenade" with the acoustics of this square in mind and calculated its musical impact accordingly: the sounds of the horns and trumpets echoing back and forth, the magnificent writing for the strings and the subtle chiaroscuro effects in the woodwinds. As the introductory march, the conductor has chosen to perform the first of the two marches K 335, which according to Mozart scholars form part of the "Post Horn Serenade".
Like every Salzburg serenade, K 320 also includes two Menuettos. The first begins by striking a somewhat grandiloguent note, seeming to enter in cap and gown before latching on to minor-key suspensions and softtoned interiections. In the Trio the flute and bassoon hold a lively dialogue to the accompaniment of the strings. This miniature wind duet affords a foretaste of the great two-movement Concertante for woodwinds and orchestra that Mozart placed at the heart of the serenade. In Salzburg it was usual to include such concerto movements within the symphonic framework of Finalmusik. Mozart had already availed himself of this tradition when including miniature violin concertos in his earlier serenades, but on this occasion he wrote a veritable sinfonia concertante for six woodwind instruments, namely, two flutes, two oboes and two bassoons. It consists of two movements in G major accompanied only by horns and strings, a piece within a piece that Mozart later performed in Vienna as a separate work in its own right. In the Andante graziaso the woodwinds interrupt the galant theme in the strings, suggesting a repeated attempt to parley in semiquavers and trills but also including sweet-toned melodic phrases in the empfindsam style. Mozart notated the dialogue for all six instruments right down to the very last detail, up to and including the brief final cadenza, providing a musical counterpart to the conversations between all of the Salzburg students who still had so much to tell one another before they left the town. This note is continued in the conversational tone of the following rondo, an Allegro ma non troppo, whose theme is first stated by the first flute and first oboe, resulting in something approaching a movement from a double concerto. But the other four wind instruments, too, keep joining in the conversation.
After such a sustained and carefree dialogue, the theme of the following Andantino is surprisingly serious. The first violins enter in their lower register with a melancholy cantilena in D minor on which the oboes and bassoons comment with a series of anguished interjections. As always with Mozart, the performance marking "Andantino" implies a slower tempo and a more emotionally charged kind of writing than an ordinary Andante. After this tearful intermezzo the second Menuetto turns emphatically to the idea of impending departure, a shift clear from the lively momentum of the middle voices. The two Trios include a number of surprising sonorities, first of which is the use of a piccolo that whistles a simple song to itself in the manner of a Salzburg coachman, after which we hear the signal of the post horn. Now there is no holding back any longer, and the three hundred bars of the presto finale tell of only one thing: the students' departure from Salzburg. In the second subject the violins seem to be waving the departing students goodbye.
Mozart's great Salzburg serenades contain a cornucopia of multiple movements, sometimes prompting him to recycle them as four-movement symphonies. This was the basis of his "Haffner" Symphony K 385 that he completed in Vienna in 1783. The previous year his father had asked him to write one last serenade for Salzburg, where Mozart's childhood friend, Sigmund Haffner, was to be raised to the nobility. Mozart duly obliged, even though the recent success of Die Entführung aus dem Serail had left him with a mountain of new commissions. He sent the first Allegro to Salzburg on 27 July 1782 and four days later was already promising "the two Menuettos, the Andante and the final movement". By 7 August he had added "a brief march". The first and final movements have survived, together with the Andante and one of the Menuettos, in the familiar form of a symphony - in his autograph score Mozart calls it a "Synfonia".
The title of the "Haffner" Symphony is also authentic. Mozart wrote to his father on 15 February 1783: "The New Hafner [sic] Symphony has really amazed me - I'd forgotten all about it; - it's bound to be highly effective." Seven months after he had completed the serenade Mozart saw the score once again and could no longer remember a single note of it, his obligations in Vienna having filled every available minute of his time. He was able to make good use of the four main movements of the serenade for his concert on 23 March. He added flutes and clarinets to the outer movements and struck out the repeat of the exposition in the opening movement. The Andante and Menuetto remained unaltered. At the first performance the first three movements opened the programme, the final movement serving to round off the concert. All four movements did indeed prove "highly effective".
"The first Allegra must be really fiery, the last as fast as possible," Mozart had written to his father on 7 August 1782. The spirit and fire of the opening Allegro con spirito are the result not only of the rushing scales in the strings but also of the majestic octaves in the first subject, followed by a march-like rhythm in the horns that ends with a descending fourth. Here Mozart was evidently reminded of a theme by Johann Christian Bach, namely, the introductory Spiritoso from the Symphony in E flat maior op. 18 no. 1. He added the octave intervals that run like a leitmotif through the movement as a whole, sometimes sounding in the first violins, sometimes occurring as an inner voice in the violas and sometimes striking o moajestic note in the basses. In the development section the violins play a minor-key counterpoint over the theme, while the winds add their plaintive commentary in the form of sigh-like seconds.
This densely structured opening movement is answered by on Andante with a loosely structured and graceful G major cantilena in the strings embedded in wonderful writings for the winds. The violins' long legato lines waft their way through the movement like the whispering breezes in Belmonte's aria "O wie ängstlich" in Die Entführung aus dem Serail. The symphony's closeness to this last-named opera is also clear from the next two movements: the Menuetto begins by striking a peremptory note reminiscent of the Pasha Selim before whom Konstanze seems to bow down in bashful modesty, while the rondo theme of the final movement is derived from Osmin's aria "Ha! Wie will ich triumphieren". But on this occasion the blaster of the harem's overseer is turned into the piquant interplay between piano and forte. Mozart's second theme is a Viennese gavotte that acquires a surprisingly serious character in the development section. The coda opens with a sophisticated web of chromatic suspensions and short appaggiaturas. In Vienna Mozart had picked up a number of novel orchestral effects from the Singspiel and opera buffa. Above all, however, he was now adept at handling the "tragicomic" element that Christian Friedrich Daniel Schubart had identified as tvpical of the Viennese style.