In a letter to his friend Abbé Joseph Bullinger, Mozart jokes about the musical environment in Salsburg. One of his subjects is the search for an additional final principle singer. “I can hardly believe it!” he wrote “A female singer!? When we have so many already! – and all of them first rate…” (1). Mozart then ponders, in the event all the principle female singers were indisposed (pregnant, taken to jail, flogged, beheaded, snatch up by the devil), a production could still proceed by using the castrato:

of course, the chapter [clergy] would object, but objecting is not as bad as rejecting – besides, no one worries much about the gentlemen of the clergy. So then, in the meantime, we’ll allow Herr Ceccarelli [a castrato in Salzburg] to change back and forth between his male and female roles. In the end, because I know at Salzburg they love variety, change, and innovation, I can see before my eyes a large field of opportunities whose realization can truly make History. My sister and I practiced it a little when we were children, just imagine what adults could do with this idea? – Oh, there are no limits to those who think imaginatively – I’m certainly not worried – and I will gladly take on the task of bringing Metastasio from Vienna, or at least make him an offer, to write several dozen operas in which the male lead and the female lead never encounter each other on stage, for in this way the castrato can play both the male and female lover in one performance, and the piece would be found especially interesting because it allows us to admire the virtuousness of the two lovers, which goes so far that they deliberately avoid speaking to each other in public. – There are have the opinion of a true Patriot! (2)

(1) Mozart, in a letter to Abbé Joseph Bullinger, 7 August 1778. Cited in: Spaethling, Robert (2000) Mozart’s Letters; Mozart’s Life. London: Faber and Faber, p.181.
(2) Ibid., p.181-2.