 The use of numerals to indicate accompanying sonorities in accompaniment parts began with the earliest operas, composed by Cavalieri and Giulio Caccini.These new genres, just as the polychoral one probably was, were indeed made possible by the existence of a semi- or fully independent bass line.In turn, the separate bass line, with figures added above to indicate other chordal notes, shortly became "functional", as the sonorities became "harmonies", (see harmony and tonality), and music came to be seen in terms of a melody supported by chord progressions (homophony), rather than interlocking, equally important lines that are used in polyphony.