A Notre Dame conductus from sometime around 1200. I'm worn out from writing admissions essays.
This is haunting -- only the most perfect consonances were treated as such; octaves and fifths are very common. I am reminded of Arvo Part's thinking in which he grants each line its own identity. Here, the upper voices are not tied to functional harmony, so the lower melody does not implicitly bear the burden of chordal roots.
Update: It occurs to me that this type of piece would make excellent listening directly prior to any appreciation of J.S. Bach; the independence of voices and the implicit assumption of their absolute equivalence was still paramount in his day; it was only later that the movement of harmonies would truly become the predominant vehicle of music.