The Serenade for Orchestra No. 9 in D major K. 320, Posthorn, was written by Wolfgang Amadeus Mozart in Salzburg, in 1779. The manuscript is dated 3 August 1779 and was intended for the University of Salzburg's "Finalmusik" ceremony that year.[1]
The serenade is scored for 2 flutes, piccolo, 2 oboes, 2 bassoons, 2 horns, 2 trumpets, post horn, timpani and strings. It has seven movements:
The Concertante and Rondeau movements feature prominent concertante sections for flutes, oboes, and bassoons. These were performed on their own in a concert in the old Vienna Burgtheater on 23 March 1783, along with the Haffner symphony, an aria from Idomeneo, and several other works.[2]
The first trio of the second minuet features a solo piccolo (called "flautino" in the manuscript) played over strings. The second trio of the second minuet features a solo for the post horn. This solo gives the serenade its nickname.
A typical performance lasts approximately 45 minutes.