Early films from the 1890s contained only single shots with no editing. Robert W. Paul's 1898 film Come Along Do! contained one of the first edits. Edwin Porter pioneered continuity editing in films like 1903's Life of an American Fireman, connecting shots across time and space. D.W. Griffith developed narrative film and continuity editing further in films like 1915's The Birth of a Nation. Soviet filmmakers like Lev Kuleshov and Sergei Eisenstein developed montage theory, using rhythmic editing to create new meanings from unrelated shots. The introduction of sound in the late 1920s posed new challenges for editors to sync sound and picture. Classical Hollywood style relied on invisible continuity editing throughout the 1930s-1950s