In the Roman Catholic Eucharist, the Agnus Dei ("Lamb of God") is sung during the fraction rite when the consecrated bread is broken and the wine poured. According to the Liber pontificalis (ed. L. Duchesne, 1:376) it was Pope Sergius I (687–701) who first ordered that during the fraction rite, the clergy and people should sing "Lamb of God [Agnus Dei], who take away the sins of the world, have mercy on us." (In the Ambrosian Rite a variable confractorium is chanted at this point in the liturgy). According to J. Froger, it is possible that Pope Sergius did nothing more than replace a variable chant in the earlier Roman liturgy with this fixed formula. M. Righetti (Manuale di storia liturgica, 3:444 and n.81), on the other hand, insists that the variable texts for the Fraction contained in many early Roman documents are of a later Gallican origin (see gallican rites). Thus, up to the time of Pope Sergius the Roman rite Fraction would have been carried out in silence. The Capitulare (ed. Silva-Tarouca, 200), which dates from a few years after the prescriptions of Pope Sergius, states that the Agnus Dei was to be sung by the entire assembly. Soon afterward, however, the Ordo Romanus I (ed. M. Andrieu, Les Ordines Romani 2:101) and the Ordo of St. Armand (ed. M. Andrieu, 2:165) directed that the clergy or the schola cantorum (also composed of clerics) were to sing the Agnus Dei. It seems, therefore, that by the second half of the eighth century it was a chant reserved to the clerics.
The phrase "quitollis peccata mundi, miserere nobis" is found also in the Gloria; both texts, however, are based on the testimonial of John the Baptist (Jn 1.29) with two grammatical changes. The vocative form "agnus" is treated as indeclinable because of a sense of reverence for religious terms. The plural "peccata" is substituted for the Biblical "peccatum." The phrase "dona nobis pacem" does not occur in any of the ancient texts. The petition "miserere nobis" was always the same, and the entire invocation was repeated as often as needed until the fraction was finished.
When multiple fractions disappeared in the ninth century, the petitions were gradually reduced to the hallowed number three. According to classic Roman usage, only one all-inclusive petition, "miserere nobis," was added to the invocation. Around the tenth and eleventh centuries the petition "dona nobis pacem" was substituted as the third and final response. The first occasion for this substitution was most probably the transfer of the Agnus Dei to accompany the Kiss of Peace (see Rabanus Maurus, De inst. cler. 1:33; Patrologia Latina, ed. J. P. Migne, 107:324). As early as the eleventh century the words "dona eis requiem" were found in requiem masses, while the third petition closed with "requiem sempiternam."
The oldest melody for the Agnus Dei (Mass 18 in the Graduale romanum ) is identical to that given for the
same text in the Litany of the Saints. The only change is the addition of a note on the accent of "nobis" in the Mass melody. The "Agnus Dei" at the end of the litany is a self-sufficient song, giving a festive climax to the litany. The dating (twelfth century) given in the Graduale romanum for the Agnus Dei of Mass 18 is very misleading, since it refers to the earliest MS in which this melody is found; whereas the melody is actually of a much earlier origin. According to A. Gastoué (Le Graduel et l'antiphonaire 278), it is related to ancient Byzantine psalmody. The Agnus Dei in the Mass of the Dead is an adaptation of that of Mass 18. This melody is known as the minor in a twelfth-century Rheinau MS, to distinguish it from a more complex one (the major ) in the same MS, destined to be sung by the schola on great feast days [M. Gerbert, De cantu et musica sacra (St. Blasien 1774) 1.1:457].
The simple Agnus melodies (Mass 18, Mass of the Dead, Mass 16) show a structural relation to the simple Sanctus melodies (Masses 15, 16, 18) by their use of recitative patterns. Just as these simple Sanctus melodies are an extension of the dialogue recitation of the Preface, so also the Agnus melodies are an extension of the dialogue recitation of the Pax Domini. Among the chant settings (c. 300) of the Ordinary, as B. Stäblein notes, the Agnus melodies are most often related to the Sanctus but very seldom to the Kyrie melodies (Die Musik in Geschichte und Gegenwart, ed. F. Blume, 1:150).
tropes for the Agnus Dei began to appear as early as the tenth century. Eighty-six of these have been found, consisting mostly of three verses and, in great part, hexameters. One verse was inserted each time between the invocation and the petition. The following is an example (from MS BN lat. 16823, fol. 1.222v):
Agnus Dei … Fons indeficiens pietatis— Miserere nobis. Agnus Dei … Actor summe bonus bonitatis—Miserere nobis. Agnus Dei … Pax eterna dator claritatis—Dona nobis pacem.
In the wake of the Vatican II liturgical reform, the Agnus Dei was restored to its original usage as an expandable litany to cover the entire fraction rite. Many vernacular musical settings in expandable litany form with variable invocations of the Lord's name have been introduced in different parts of the world.
Bibliography: j. froger, Les Chants de la Messe aux VIIIe et Ixe siècles (Tournai 1950). j. a. jungmann, The Mass of the Roman Rite, tr. f. a. brunner, 2 v. (New York 1951–55) 2:332–340. General Instruction to the Roman Missal. Music in Catholic Worship. Liturgical Music Today.