Gregorian chant made use of unusual yet basic scales called church modes.
Gregorian chant, monophonic, or unison, liturgical, sacred music of the Roman Catholic Church, used to accompany the text of the mass and the canonical hours. Gregorian chant developed mainly in western and central Europe during the 9th and 10th centuries. Gregorian chants were organized initially into four, then eight, and finally 12 modes.