Beethoven often composed several major works at the same time, each a distinctly different expressive outlet. He began sketching his Fifth Symphony in 1804 but didn't complete it until four years later. The innovative construction of that piece and its unprecedented intensity are embodied in the opening four notes, the most famous theme in classical music. In the interim between the Fifth's first sketches and its completion, Beethoven wrote some of his most lyrical music-for the opera Leonore (which would become Fidelio) and the Fourth Symphony. The latter's consistent high spirits contrast starkly with the struggle against fate embodied in the Fifth.