This was not only a remarkable composition but a famous one. It is found complete on a French
manuscript leaf dating from the tenth century, but we know that it was a ninth-century composition—and
already famous in the ninth century—because its first two couplets were chosen as a didactic illustration
in Musica enchiriadis (“Handbook of music”), the earliest surviving Frankish treatise about practical
music-making, which is thought to date from some time between 860 and 900. The illustration is
reproduced in Fig. 2-2. It is one of several examples in the treatise of polyphonic singing, and can serve
us as a forceful reminder that polyphony was routinely practiced among the Franks as early as we have
any evidence of their musical practice at all.
In this arrangement (transcribed in Ex. 2-6), the upper voice sings the original Rex caeli melody, for
which reason it is called the “principal voice” (vox principalis). The lower voice, called the vox
organalis because it produces the harmony or counterpoint (called organum at the time), begins at the
unison and holds on to its initial pitch as a drone until the principal voice has reached the interval of a
fourth above it, the smallest interval considered consonant according to the theory of the time. At this
point, the two voices move in parallel until the cadence (or occursus, as it was called, meaning the
coming-together), which restores the unison. In the second phrase, the augmented fourth against B is
avoided first by sustaining the “organal” G, and then by leaping to E. Once again unison is restored at the
end.