Léonin

Léonin is the first major composer of music for multiple voices whose name has come down to us. He worked in Paris in the second half of the 1100s, attached to the cathedral of Notre Dame while it was still under construction, and was likely a poet and cleric there as well.

Almost everything we know about him comes from a single source: notes by an anonymous English student written a century later, which credit Léonin with compiling the Magnus Liber, the "Great Book" of chant settings in which a second voice soars in long, flowing lines above the slow notes of the traditional melody. It was a decisive step: music with independent parts sounding together, written down so it could be repeated and built upon.

There is no standard single work to name, so start with any good recording of the Notre Dame school's music from the Magnus Liber and let the open, ringing sound of the twelfth century wash over you.