The trombone has been used in jazz ensembles since the beginning of jazz. In early jazz styles, its role was often to "comp" behind the lead instrument by playing improvised counter lines. During the swing era, trombones were an essential part of the big band. When bebop came around, trombones became less common, owing to the fact that it is simply more difficult to play sinewy lines than on other instruments. Because of its power and its unique tone, the trombone is frequently used in many stylistic veins.