The Classical period also saw the gradual development of sonata form, a set of structural principles for music that reconciled the Classical preference for melodic material with harmonic development, which could be applied across musical genres. The sonata itself continued to be the principal form for solo and chamber music, while later in the Classical period the string quartet became a prominent genre. The symphony form for orchestra was created in this period (this is popularly attributed to Joseph Haydn). The "concerto grosso" (a concerto for more than one musician), a very popular form in the Baroque era, began to be replaced by the "solo concerto", featuring only one soloist. Composers began to place more importance on the particular soloist's ability to show off virtuoso skills, with challenging, fast scale and arpeggio runs. Nonetheless, some "concerti grossi" remained, the most famous of which being Mozart's Sinfonia Concertante for Violin and Viola in E-flat major.