This was Beethoven’s 13th sonata and it was written in 1800/01. It was published separately from its more well-known ‘sister’ sonata, Op. 27 no. 2, the “Moonlight” sonata but at the same time. It was dedicated to Princess Josephine von Liechtenstein.
The movements are not in the usual order for a sonata, the first movement is a slow movement. There is much contrasting material between the movements and the first movement is not in sonata form.
Beethoven gave this sonata the surprising title “Sonata quasi una Fantasia”. It is thought that the name is derived from the fact that there are no breaks in between movements and the unusual order of the movements. The order is slow-fast-slow-fast.
The following is by David Gross from the website www.classicalconnect.com ‘Throughout his life, Beethoven continued to make contributions to the genre of the piano sonata. He never stopped developing its form, seeking new levels of expression and scope. The title of the sonata Op. 27 No. 1 "Sonata quasi una fantasia" already suggests an unusual form and intensity of expression. Beethoven abandons the expected sonata scheme by opening with a slow movement, by returning to themes at surprising times, and by blurring divisions between movements. The sonata ends with a boisterous Allegro that combines features of sonata and rondo form’.
www.classicalconnect.com/Piano_Music/Beethoven/Sonata_No._13/1276
www.wikipedia.org