...there was the Notre Dame School:
This is "Sederunt principes," by Pérotin, aka Magister Perotinus, aka Perotinus Magnus - believed to have been composed for performance in the unfinished Cathédrale Notre Dame de Paris on the feast day of St. Stephen (the day after Christmas), 1199.
This is Western "polyphony" (i.e., music where more than one voice sounds at the same time) in its first full, glorious, flower.
There are a number of excellent recordings of the music of Perotinus available. I most strongly recommend the one by Antony Pitts & his brilliant ensemble Tonus Peregrinus on the Naxos label.