FIG. 2-2 Rex caeli Domine, a sequence-like hymn probably dating from the ninth century. (a) Its most complete source, a
French manuscript from the tenth century written in an alphabetic notation that specifies pitch precisely. (b) Its earliest source,
the ninth-century treatise Musica enchiriadis, which shows a fragment of it, in a similar notational style, adapted to illustrate a
common practice whereby monophonic chants were amplified polyphonically in performance. This provides evidence of
polyphony as early as any evidence of the chant itself.
EX. 2-5 Rex caeli Domine (Fig. 2-2a) transcribed