This lecture focuses on the changing role of music in the medieval world. Roman Catholic liturgical plainchant dominated the music of the so-called Dark Ages. With the gradual return of civilization to Europe during the High Middle Ages also came the development of composed polyphony, called organum, including a type of organum known as florid organum. Florid organum is exemplified by the music of Leonin, a composer of the Ars Antiqua school. The violent disruptions of the 14th century—the so-called Babylonian Captivity, the Great Schism, the Black Death, and the Hundred Years’ War—led to a rise of secularism, the cultural impact of which could be seen in a new vernacular literature and the beginning of the Humanism movement. The new music, known as Ars Nova, was characterized by isorhythm; Guillaume de Machaut was the most representative composer of this new style.