Twelfth-century composers, such as Léonin and Pérotin developed the organum that was introduced centuries earlier, and also added a third and fourth voice to the now homophonic chant.
Композиторите од 12 век, како Леонин и Перотин го развиле органумот што бил користен векови претходно, и му додале трет и четврт глас.