Mozart composed his last three symphonies in the summer of 1788 in the unbelievably short space of a mere six weeks. He wasn't on commission and there was no "external reason" (other than, perhaps, to try to overcome his financial difficulties and to distract him from "dark thoughts") for him to work at such immense speed. There's some uncertainty as to whether these symphonies were performed during Mozart's lifetime. Once they were known, thought, audiences were quick to recognize in them a pinnacle not only of Mozart's work but in the entire field of instrumental music.
For anyone who is wild about Mozart, I recommend The Times Online's Mozart 250th anniversary special dossier.
The following article was taken from today's Daily Telegraph:
The 250th anniversary of Wolfgang Amadeus Mozart's birth, which falls today, is an occasion for saluting the awesome scope of his achievement.
By the age of five, he was not merely performing in public, but also composing. His juvenilia stands up against the mature works of most composers. He had one talent in his short life - he died aged just 35 - that caused his reputation to survive so well, and to spread so widely, over the subsequent centuries.
He is, and always was, what is now called "accessible". Lest that word seem derogatory, let us add that Mozart's accessibility was of a rare order. He wrote music of immediate beauty to the undiscerning, and which impresses sophisticates with its inventiveness, innovation and sheer musicality. It is no wonder he inspired such jealous loathing among some of his inferior contemporaries.
Some dismiss Mozart as facile: he certainly could write with ease and to order, and had to keep body and soul together. Yet his facility does not indicate sterility, as it has in others with such a gift, but rather proves his unequivocal genius.
The last three symphonies; some of the piano concerti, notably the 21st; the chamber music for strings, including the six "Haydn" quartets, which prompted the dedicatee, no slouch himself, to tell Mozart's father that his boy was the greatest composer in the world: all are masterpieces with few rivals in the whole canon of music.
In the theatre, Mozart showed himself as adept with opera seria as with opera buffo. His range is stunning, and unmatched by any other composer, however long-lived.
Genius is rare in music as in all other arts. Perhaps Britain has only produced one - Benjamin Britten, whose originality and prodigious talent make him the closest we have ever come to having a Mozart.
In the rest of Europe, perhaps only Bach, Haydn, Beethoven, Wagner and Mahler could make a claim for parity - though France might offer up Ravel and Russia Tchaikovsky. That Mozart might see any of them off in a celestial all-comers bout is hard, though, to gainsay.
But while we rate his conspicuous genius, one factor is perhaps a more significant reason for our choosing to celebrate him so warmly today: that, when all is said and done, he remains the greatest entertainer.