According to the Internet source given below, Leoninus wrote both poetry and music. Among his accomplishments as a poet was the setting of the first eight books of the Old Testament as hexametric verse. However, today he is chiefly remembered for his contributions as a composer of polyphonic liturgical music. While most composers of this genre were anonymous, Leoninus is credited with having written the Magnus liber organi
(The Great Book of Organum), a work that notated Leoninus's sacred polyphonic compositions and which greatly influenced western musical practices for the next several hundred years.
||Brief biography by www.musicacademyonline.com