INTROIT. — This is the name in the Roman liturgy of the chant performed while the celebrant, in Solemn Mass, proceeds to the altar. Like the invitatory in the Divine Office, it interprets and expresses the sentiments proper to the mystery or feast of the day.
The Gelasian Sacramentary of the 8th century calls it “antiphona ad introitum” (cf. also the Roman Ordo I [n. 8], II [n. 3], III [n. 8] and the Ordo Ioannis Archicantoris); the Gregorian Sacramentary of Adrian gives it instead the name “introitus,” and Roman Ordo V (11th century) that of “invitatorium.”
The Liber Pontificalis (I, p. 230) attributes its institution to Celestine I (422–32), but the passage is unclear and it is uncertain whether it refers to the Introit or rather to the chanting of the psalms of the vigils before the Sacrifice. Hence Probst assigns its origin to Gelasius (492–96), while Battifol places its introduction in the 15th century.
The Introit originated as a chant of the schola, not of the assembly. This explains the richness of its melody, quite different from the recitative style of chants intended for the congregation.
Roman Ordo I (nn. 40 ff.; M. Andrieu, Les Ordines romani, II, Louvain 1948, p. 80) describes the singing of the Introit thus: the chanters are arranged in two rows before the altar. When the Pope emerges from the secretarium, the precentor (prior scholae) intones the antiphon, which is sung first by the first choir and then repeated by the second. Next the first choir sings the verses of the psalm, alternating with the antiphon-refrain, always sung by the second choir. When the Pope reaches the altar, the Gloria is sung, followed by the versus ad repetendum (a characteristic verse which had determined the choice of the psalm), sung by the first choir, while the second concludes with the repetition of the antiphon. This solemn performance was later simplified in parish churches and monastic oratories, where the clergy was scarce. The psalm was reduced to one or two verses. Then even the antiphon after the verses was repeated only in part (at Cluny in the 11th century: PL 149, 653), until it disappeared altogether, leading to the present arrangement as sanctioned by the Missal of Pius V (1570). The abbreviation Ps(almus) instead of V(ersus), still found before the verse, recalls the primitive form of the Introit. Pius X (Graduale Romanum, Rome 1907) restored the custom of singing the Introit “as the priest approaches the altar,” and the Sacred Congregation of Rites has recently granted the faculty of singing it “more antiquo” (cf. Ephem. lit., 62 [1948], pp. 248–55).
The principal source of Introits is the Psalter. Others derive from Scripture readings (the most ancient), from free composition, e.g., Salve sancta Parens by Sedulius; Gaudemus by St Gregory (d. 604), or from other sources such as Aciplicite iucunditatem of the Tuesday after Easter, and the Requiem of the funeral liturgy, considered by Morin among the most ancient because drawn from the book of Esdras, excluded from the canonical books in the 4th century. Centonization is not rare, as in the Easter Introit Resurrexi. In the Middle Ages tropes were also added to Introits (v.), but all have disappeared.