by 1795-96, with his Op. 1 piano trios and Op. 2 piano sonatas, Beethoven had started developing a style which not only displayed an increasing mastery of the Viennese style but also contained a dramatic flair which became a quintessential feature of his music (These works are in the four-movement sonata form, more often associated with orchestral symphonies rather than chamber works or piano sonatas). In particular, the 1st movement of his first piano sonata displays an intensity in musical construction that foreshadows the motivic development he would later exploit in his 3rd and 5th symphonies, while the piano trio in C minor had such an intensity of expression that Haydn thought that they would not be understood by the public. In addition, these works also display virtuosity which would become another of Beethoven's characteristics, particularly in his piano sonatas and chamber works. In addition, Beethoven also developed a penchant for the key of C minor which would last for the rest of his life. Most of his full-scale works in minor keys from this period are in the key, including the 'Pathétique' sonata (the 1st movement of which was novel in its integration of the slow introduction into the overall sonata form), and the key became a byword for extreme drama in Beethoven's works. Beethoven also seemed to have an interest in all current musical genres, including three piano concertos (the 2nd, in B-flat major, being a revised version of a piano concerto from his Bonn years), some violin and cello sonatas, and the Op.18 string quartets. The latter in particular illustrates Beethoven's increasing interest in 'motivic saturation (in the first movement of the 1st quartet in F major and juxtaposition of strikingly different moods (in the Finale of the 6th quartet in B-flat major, subtitled 'La malinconia'), the latter of which is a precursor to similar explorations in his late period. Beethoven became increasingly more experimental in his use of form in his piano sonatas of 1800-02. Op. 26 in A-flat major contained a 'marcia funebre' which foreshadows that of the 'Eroica' symphony; Op.27 no. 2 in C-sharp minor 'Quasi una fantasia' (the famous 'Moonlight' sonata), where the dramatic sonata form movement comes last instead of first; and Op. 31, No. 3 in E-flat major. This formal experimentation furthered his incorporation of differing moods into the sonata style that had already been seen in the finale of Op.