Not surprisingly music changed dramatically between the years 600 and 1600. Perhaps the two most notable developments are the invention of musical notation and development of harmony. Music was one of the branches of the quadrivium. While the nature of music in Western Europe underwent radical change, there were a number of remarkably long lived concepts. The theories of Guido of Arezzo were still being taught in the seventeenth century, and the Pythagorean scale still held sway until Bach's Well Tempered Clavier.