Sigismund Haffner the Younger was getting his spurs from the Emperor, and he decided to celebrate the occasion the same way he celebrated his sister's wedding a few years before: by commissioning Wolfgang Amadeus Mozart to write a serenade.
Mozart at the time was swamped. He had so many irons in the fire that he didn't see how he could possibly squeeze this in, but he managed: a serenade with a march at the beginning and a pair of minuets in the middle.
But he remained so busy, that no one is entirely sure if the serenade made the ceremony!
What we are sure of is that that serenade makes some great leftovers. Lop off the march, extract one of the minuets and you have a great 4-movement symphony on your hands: the Haffner.
MUSIC: Mozart: Haffner Symphony; Koch 7574