Musica enchiriadis

"Musica enchiriadis," written around the 9th century, is a foundational text in the history of Western music theory. It serves as a guide for understanding and performing music, particularly focusing on early polyphony—where multiple independent melodies are sung or played simultaneously. The treatise introduces concepts such as intervals, harmony, and the practice of adding harmonies to a melody. Its significance lies in shaping the way music was composed and understood in medieval Europe, bridging the gap between monophonic chant and more complex musical structures that followed.