Medieval

When we explore Medieval music, we are dealing with the longest and most distant period of musical history. Saint Gregory is credited with organizing the huge repertory of chant that developed during the first centuries of the Christian church, hence the term Gregorian chant. He was pope from 590 to 604, and the Medieval era continued into the 1400s, so this period consists of almost a millennium's worth of music.
One of the principal difficulties in studying Medieval music is that a system for notating music developed only gradually. The first examples of musical notation date from around 900. For several centuries, notation only indicated what pitch (or note) to sing. The system for notating rhythm started in the 12th or 13th century.
Gregorian chant is monophonic, meaning music that consists of only one melodic line without accompaniment. The beauty of chant lies in the serene, undulating shapes of its melody. We do not know who wrote the melodies of Gregorian chant. Like folk melodies, the music probably mutated as it was passed down through generations and eventually reached its notated form.
Polyphony, music where two or more melodic lines are heard simultaneously, did not exist (or was not notated) until the 11th century. Unlike chant, polyphony required the participation of a composer to combine the melodic lines in a pleasing manner. Although most Medieval polyphonic music is anonymous--the names of the composers were either lost or never written down at all--there are composers whose work was so important that their names were preserved along with their music.