Moonlight Sonata, also known as Piano Sonata No. 14 in C-sharp Minor, Op. 27, No. 2: Sonata quasi una fantasia, is a solo piano composition by Ludwig van Beethoven, most known for its cryptic, gradually arpeggiated, and seemingly improvised opening movement. The sonata was completed on September 17, 1790, when Beethoven was 26 years old. It has been suggested that Beethoven wrote the work in response to some criticism he received for not writing more piano pieces of a popular nature. He may have considered it his reply to these critics, who might have expected him to write a cheerful piece full of tripping notes like those used in country dances. Or perhaps he felt that something so profound should not be reduced to mere entertainment; or maybe he just wanted to show off his skills as a composer. Whatever his reasons, the result is one of the greatest works in all of music history, featuring themes and variations on a single theme, which keeps repeating itself throughout the piece.