The viola plays an important role in chamber music. Mozart used the viola in more creative ways when he wrote his six string quintets. The viola quintets use two violas, which frees them (especially the first viola) for solo passages and increases the variety of writing that is possible for the ensemble. Mozart also wrote for the viola in his, Sinfonia Concertante, a set of two duets for violin and viola, and the Kegelstatt Trio for viola, clarinet, and piano. The young Felix Mendelssohn wrote a little-known Viola Sonata in C minor (without opus number, but dating from 1824). Robert Schumann wrote his "Märchenbilder" for viola and piano. He also wrote a set of four pieces for clarinet, viola, and piano, "Märchenerzählungen".