Serenade No. 9, Posthorn K. 320

The term serenade may bring to mind sweet melodies sung by a suitor under a window but, since the 18th century, it also suggests lighthearted ensemble music to be performed in the evening, especially at an outdoor public gathering. Mozart was a master of the former style—Don Giovanni, for example, sings a dashing serenade to a maid—but it is the instrumental genre upon which Mozart left a revolutionary stamp. Since most serenades were created for specific festivities, often to be used only once, composers too often dashed off generic, forgettable works. From early in his musical maturity, Mozart defied that trend, elevating the serenade to the sophistication of the concert hall while retaining the form’s airy, celebratory spirit. It is no surprise that Mozart successfully retooled some of his most ambitious serenades into symphonies, most notably the “Haffner” Symphony, recycled after its initial use at the wedding of a family friend.

The Serenade No. 9 is one of the latest and largest of Mozart’s outdoor evening works. He probably wrote it for the annual graduation ceremony of the University of Salzburg, and the size of the ensemble suggests that he needed to reach a particularly large crowd. The timpani and cellos would have waited on stage while the rest of the ensemble, with their more mobile instruments, entered and exited performing special marches written for the occasion.

The Serenade’s nickname comes from the final contrasting Trio section in the second Minuetto, in which Mozart called for a posthorn to play the characteristic calls that announced the arrival of the mail. (In a modern echo of that tradition, German mail receptacles still bear an icon of the cylindrical horn.) Other important musical factors that define this work are the long, surging crescendos—a signature sound of the famous orchestra in Mannheim where Mozart had spent several months in 1777—and the inner movements that create a mini Sinfonia Concertante for flutes, oboes and bassoons.