Though mostly associated with the Swing era, big bands have been a part of every period in jazz. Count Basie's outfit defined Swing in the freewheeling 1940s and the streamlined '50s. Duke Ellington worked in popular music but used his orchestra to explore many artistic directions. Shorty Rogers led a Cool big band, and Dizzy Gillespie led a dynamic Bop orchestra. Gil Evans gained fame by backing Miles Davis with his sweeping tonal colors while the Soul Jazz sound of Jimmy Smith hit the charts with the help of booming ensembles. The great expense of keeping big bands together has made them rare in modern times, but rekindled interest in the Swing era has numerous regional orchestras keeping the tradition alive.