"Ut queant laxis" or "Hymnus in Ioannem" is a Latin hymn in honor of John the Baptist, written in Horatian Sapphics[1] with text traditionally attributed to Paulus Diaconus, the eighth-century Lombard historian. It is famous for its part in the history of musical notation, in particular solmization. The hymn belongs to the tradition of Gregorian chant.
It is not known who wrote the melody. Guido of Arezzo possibly composed it,[2] but he more likely used an existing melody. A variant of the melody appears in an eleventh-century musical setting of Horace's poem Ode to Phyllis (4.11) recorded in a manuscript in France.[3]