Of the 134 symphonies mistakenly attributed to Haydn that H. C. Robbins Landon lists in his catalog, 33 are in C major, more than any other key.

Before the invention of the valves, Haydn did not write trumpet and timpani parts in his symphonies, except those in C major.

Landon writes that it wasn't "until 1774 that Haydn uses trumpets and timpani in a key other than C major... and then only sparingly."

Most of Haydn's symphonies in C major are labelled "festive" and are of a primarily celebratory mood.

[5] This idea is further explored in a radio program called The Signature Series.