Ut queant laxis
Ut queant laxis is the first verse of the hymn to Saint John the Baptist, written by Paulus Diaconus in the VIII century, a Benedictine monk and Lombard historian. Saint John the Baptist is the Jewish prophet of Christianity.
This verse is known because from here comes the name of the musical notes. Guido d'Arezzo used the first syllable of each verse, except the last: ut, re, mi, fa, sol, la. Centuries later, Anselmo of Flandes introduced the name si for the missing note, combining the initials of Sancte Ioannes. Later in the XVII century the Italian musicologist Giovanni Battista Doni replaced the note ut for do, because this facilitated the solfege syllable because it ends in a vowel. He noted that it was difficult to solfege with the note ut because it ends in a consonant, and had the idea of replacing it with the first syllable of his own name (do) for easy pronunciation. Another theory is that perhaps comes from the word Dominus, Lord in Latin.
In conclusion, for me as a musician is curious to know from where musical notes come. Their names are very old.