Early in the 11th century, Guido d'Arezzo used the lyrics of this song to name the notes of the scale: Ut-Re-Mi-Fa-Sol-La-Si, which was later revised to the Do-Re-Mi-Fa-So-La-Ti we use today. Notice how the first six phrases in the melody start on the first six notes of the scale.
Ut queant laxīs
resonāre fibrīs
Mīra gestōrum
famulī tuōrum,
Solve pollūtī
labiī reātum,
Sāncte Iohannēs.