In 1853 the French romantic composer Charles Gounod wrote a melody that was especially designed to sit over the Prelude No. 1 in C Major written by Johann Sebastian Bach over a century earlier. He titled it (somewhat unimaginatively, perhaps) "Meditation sur le Premier Prelude de Piano de S. Bach."
Interestingly enough, Gounod's father-in-law, the magnificently named Pierre-Joseph-Guillaume Zimmerman, transcribed the improvised melody and arranged it for violin, piano, and harmonium; and thus a piece that Gonoud himself never actually wrote down went on to become one of the most-recorded and most-played pieces of music in the history of mankind.