It includes large-scale works that express heroism and struggle. Middle-period works include six symphonies (Nos. 3–8), the last three piano concertos, the Triple Concerto  and  violin concerto , five string quartets (Nos. 7–11), several piano sonatas (including the  Moonlight ,  Waldstein  and Appassionata  sonatas), the  Kreutzer  violin sonata and Beethoven's only opera