What led to the birth of polyphonic music?

The Notre Dame school trained a lot of famous singers in the Middle Ages. They were the first group of composers to bring Polyphony into the church. They cataloged a significant amount of music do that is why we know so much about music from the Middle Ages today.

the correct answer for this question is:

it is system invented in 1872 that produced the first illusion of movement. basically it was a disk with a series of drawings around the edge, showing the same object in slightly different poses. when it was spun, it created the illusion of movement.

found this online : )