Who were Léonin and Pérotin?

Léonin and Pérotin were significant figures in the development of early polyphony, particularly associated with the Notre Dame School of polyphony in the late 12th and early 13th centuries. Their contributions marked critical advancements in the use of multiple independent melodies, which was a departure from the monophonic textures that predominated medieval music before their time. Léonin is often credited with developing organum, where a plainchant melody is complemented by an additional melodic line, while Pérotin expanded on this by introducing richer, more complex textures involving up to four voices. Their work laid foundational principles for the evolution of Western music, influencing the use of harmony and counterpoint in music that followed. The other options pertain to areas outside their contributions, highlighting their pioneering role specifically in polyphonic music rather than secular rhythm, opera, or architectural design.