<P> The Magnus Liber was intended for liturgical use . According to Anonymous IV, "Magister Leoninus (Léonin) was the finest composer of organum; he wrote the great book (Magnus Liber) for the gradual and antiphoner for the sacred service ." All of the Magnus Liber is for two voices, although little is known about actual performance practice: the two voices were not necessarily soloists . </P> <P> According to Anonymous IV, Léonin's work was improved and expanded by the later composer Pérotin . See also Medieval music . </P> <P> The musicologist Craig Wright believes that Léonin may have been the same person as a contemporaneous Parisian poet, Leonius, after whom Leonine verse may have been named . This could make Léonin's use of meter even more significant . </P>

The two most important french composers of organum during the medieval period were