Maybe, Volgadon, but in what is now Italy, it was plain song/Gregorian Chant of single melody until the Renaissance, when polyphony was developed and quickly spread throughout Europe, I think.

Wrong!

I quote from the Concise Oxford History of Music By Gerald Abraham,

"The earliest unmistakable mention of Western polyphony ... occurs in a Treatise De Institutione Harmonica by Hucbald (c 840 - 930), a monk of St. Amand in the diocese of Tournai"

Three things

The years given, approx 900 AD are a good deal earlier than the renaissance - about 500 years (give or take a few decades).

Tournai is not in Italy, it is in what is now Belgium.

Conscious use of harmony has been in use in Western music for at least 1000 years. Although it started in the church and was subsequently taken up by the aristocracy, I find it hard to believe that it did not seep out into popular music at some point.

Geoff