The earliest type of polyphony was?

The earliest type of polyphony is known as organum, which emerged in the early Middle Ages. Initially, it involved adding a second melodic line to a plainchant, typically in parallel motion at a fixed interval, often a fourth or fifth. This practice evolved over time, leading to more complex forms of polyphonic music. Organum laid the foundation for the development of Western Classical Music and the intricate polyphonic structures that followed.