A violin concerto is a concerto for solo violin (occasionally, two or more violins) and instrumental ensemble, customarily orchestra. Such works have been written since the Baroque period, when the solo concerto form was first developed, up through the present day. Many major composers have contributed to the violin concerto repertoire, with the best known works including those by Vivaldi, Bach, Bartók, Beethoven, Brahms, Bruch, Mendelssohn, Mozart, Paganini, Prokofiev, Shostakovich, Sibelius, Tchaikovsky, and Vivaldi. Traditionally a three-movement work, the violin concerto has been structured in four movements by a number of modern composers, including Dmitri Shostakovich, Igor Stravinsky, and Alban Berg (in the latter, the first two and last two movements are connected, with the only break coming between the second and third). In some violin concertos, especially from the Baroque and modern eras, the violin (or group of violins) is accompanied by a chamber ensemble rather than an orchestra—for instance, Vivaldi's L'estro armonico, originally scored for four violins, two violas, cello, and continuo, and Allan Pettersson's first concerto, for violin and string quartet.