This article summarizes one of the most significant developments in Western music history: the rise of polyphonic texture in the composition of sacred music.  The earliest forms of polyphony in Europe were called organum.  Organum reached its height at the hands of the composers at the Cathedral of Notre Dame in Paris. Leoninus and his successor Perotinus perfected a style of florid or melismatic organum that must have been astonishing to the people of their day. You’ll often see the French version of those composers’ names: Leonin and Perotin.