By the 1940s, cover versions of African-American songs were commonplace, and frequently topped the charts, while the original musicians found success among their African-American audience, but not in the mainstream. In 1955, Thurman Ruth persuaded a gospel group to sing in a secular setting, the Apollo Theater, with such success that he subsequently arranged gospel caravans that traveled around the country, playing the same venues that rhythm and blues singers had popularized. Meanwhile, jazz performers began to push jazz away from swing, danceable popular music, towards more intricate arrangements, improvisation, and technically challenging forms, culminating in the bebop of Charlie Parker and Dizzy Gillespie, the cool sounds and modal jazz of Miles Davis, and the free jazz of Ornette Coleman and John Coltrane.