When we're the first steps toward the development of polyphony taken?

The first steps toward the development of polyphony occurred during the Medieval period, particularly around the 9th and 10th centuries. Early forms of polyphony, known as organum, began to emerge as composers started adding one or more melodic lines to a pre-existing chant. This practice gradually evolved, leading to more complex structures by the 12th century with the advent of notated music, ultimately paving the way for the rich polyphonic traditions of the Renaissance.