Two great innovators of early 20th-century music, Schoenberg and Stravinsky, both wrote violin concertos. The material in Schoenberg's concerto, like that in Berg's, is linked by the twelve-tone serial method. Bartók, another major 20th-century composer, wrote two important concertos for violin. Russian composers Prokofiev and Shostakovich each wrote two concertos while Khachaturian wrote a concerto and a Concerto-Rhapsody for the instrument. Hindemith's concertos hark back to the forms of the 19th century, even if the harmonic language he used was different.