He named the note scale inspired by a hymn to Saint John the Baptist, composed by Paolo Diacono three centuries earlier. The verses in the hymn were these:
"Ut queant laxis... resonare fibris... mira gestorum... famuli tuorum... solve polluti... labii reatum... Sancte Iohannes."
As you can see, d'Arezzo adapted the last two words to form the Si. Five centuries later, though, the musician Giovanni Maria Bononcini made one last change in the scale. He excluded the "Ut" and exchanged it for "Do", from Dominus (which means "Lord"). This system, however, spread mainly to latin countries.