Q. Did medieval people sing the Rosary in Gregorian chant?

Evidently they did. Historical literature abounds with references to “singing” or “chanting” the Rosary, as distinct from “saying” or “reciting” it. For example, St. Louis de Montfort writes, “There are several ways of saying the Holy Rosary, but that which gives Almighty God the greatest glory… is that of saying or chanting the Rosary publicly in two groups (c’est de le psalmodier ou réciter publiquement à deux choeurs).” (10) Significantly, De Montfort does not use the verb chanter (“to sing”) in this passage, but rather psalmodier, a term of art specific to the singing of liturgical chant. Its literal meaning is “to Psalmodize” or to sing Psalms.