In the Ambrosian rite of mass, the distribution of communion takes place while the choir chants an antiphon called the Transitorium. On Easter day, the Transitorium is the Venite populi, shown above as it is contained in the Ambrosian Antiphoner.
The Schola Sainte Cécile recorded this Ambrosian Transitorium of Easter day as an expression of friendship with the people of Milan who are suffering through the epidemic this spring 2020:
Here is the text with an English translation:
Veníte, pópuli: sacrum immortále, mistérium illibátum agéndum cum timóre et fide. Accedámus mánibus mundis, pœniténtiæ munus communicémus: quóniam Agnus Dei propter nos Patri sacrifícium propósitus est: Ipsum solum adorémus, ipsum glorificémus cum ángelis clamántes: Hallelújah, hallelújah.
Come ye people to the holy, immortal, unspotted mystery to be performed with fear and faith. Let us draw nigh with clean hands, let us take in communion the gift of penance: for the Lamb of God was offered up as a sacrifice to the Father for us. Him alone let us adore, him let us glorify, crying out with the angels: Alleluia, alleluia.
As Michel Huglo pointed out (Les Chants de l’ancienne liturgie gallicane, 1970), the Ambrosian rite has generally made use of Roman communion antiphons for its antiphonae ad confractorium, sung during the celebrant’s fraction of the host, and employed pieces of either either Gallican or Eastern provenance for the communion (the ambrosian Transitoria). And indeed, this Milanese transitorium is found in a great number of Carolingian and medieval french manuscripts, and thus it is generally supposed that we see here a relic of the ancient rites of Gaul before their suppression by Pepin the Short and Charlemagne.
Here is the text used in France, presenting a few minor variations with the Milanese reading. The melody seen here transcribed by the Solesmes books (in Dom Pothier’s monastic Processional of 1888), and is substantially the same as that of Milan:
The piece is typical of the ancient liturgy of Gaul. Dom Edmond Martène thought it was reminiscent of a sermon of St. Cesarius of Arles, and based on a passage in the Miracles of St. Martin, composed by Gregory of Tours, which shows that the ancient rite of Gaul called the faithful to general communion on Easter day.1 The text is not taken from Scripture (as nearly all pieces in the repertoire of Roman chant) and—calling together angels and man in a common adoration— it evokes the celestial liturgy of the Apocalypse, so dear to the ancient rite of Gaul. The vocabulary employed to speak of the Eucharist (mysterium, libamen, munus) harks back to a very remote epoch, while the “clean hands” are an allusion to the communion in the rite of Gaul, where the hands were used as a paten by communicants (and woman covered them with a veil). Underneath the Latin text, however, one senses the presence of a Greek antecedent (if such a piece existed, it subsequently disappeared from the Eastern liturgies) translated into Latin, and it is possible that the Gallican and Ambrosian melodies retained the mode of the Byzantine chant. The themes of participation in the holy mysteries with fear and faith are frequently found in the Fathers of the Antiochian school.
In the liturgy of St. John Chysostom, for example, the deacon, having received communion from the celebrant’s hand, takes the chalice, goes to the royal doors in front of the iconostasis, and raising it, invites the people to come to communion proclaiming, in a text that strongly resembles our own:
Μετὰ φόβου Θεοῦ, πίστεως καὶ ἀγάπης προσέλθετε.
With the fear of God, faith and love, come forward!
It is not impossible, furthermore, that the Gallican and Ambrosian text should have been an amplification of this diaconal invitation calling the people to communion. It seems that in the ancient rite of Gaul, this text was originally chanted by the deacons before communion, and that this was its ancient position. The medieval manuscripts of the Abbey of Saint-Benoit-sur-Loire2 indicated further that the Venite populi was chanted before communion by two deacons.
This old Gallican text is found in many liturgical manuscripts3 from Tours, Poitiers,4 Vienne, Chartres, Paris, Châlons, Saint-Omer, Verdun, the abbeys of Saint-Denis, of Saint-Martin de Tours (where it is chanted on Easter day during the clergy’s communion5), of Pontlevoy (where it was chanted on solemn feasts), of Saint-Vaast d’Arras, of Saint-Martin of Autun, of Montoriol, and of Echternach.
The piece had particular prominence in the Lyonnese rite, where it passed from the manuscripts into the first edition of the Lyonnese Missal in 1487, where it was taken (after the Parisiano-Lyonnese parenthesis of Mgr de Montazet’s books6), into the Romano-Lyonnese books of Cardinal de Bonald (only for the cathedral). In the Lyonnese rite, the Venite populi is sung between the first and second Agnus Dei on Christmas, Easter, and Pentecost, which were formerly the days of the people’s general communion, when all were obliged to receive communion according to the decrees of the Council of Elvira in 305, the Council of Agde in 506 (canon 18), and the third Council of Tours in 813 (canon 50)7.
These are the rubrics relating to the Venite populi on Easter day as given by the Ordinary of Châlons:
The choir in copes comes together after the communion of the bishop or priest. The deacon and subdeacon are in front of the altar, the bishop stands apart on the right side of the altar, wearing mitre and crozier, and the cantor begins the antiphon Venite populi, which the others take up. When they come to the words Ipsum solum adoremus, everybody kneels. When the antiphon is over, the canons and clerics both the higher and lower stalls who are to receive communion receive the kiss of peace from the bishop. Then the bishop gives them communion, having removed his mitre and crozier, and also to the laymen, if there are any.
These is how the ceremony was carried out on Easter day according to the missal of the Abbey of Saint-Martin d’Anay in Lyon:
Having said the Agnus Dei, before the reception of communion, the abbot or whoever is celebrant goes to the footpace of the altar, where everyone received the peace from him. The abbot, embracing the brethren, says to each: Pax tecum frater, and the other responds, Et cum spiritu tuo. The deacon and subdeacon receive the peace first, then the eldest first. After this, the ministers turn towards the altar, and everyone then come around the altar and sing aloud the antiphon Venite populi. When they say Ipsum solum adoremus, everyone kneels, and as it is sung, two large thuribles incense the altar. Thereafter all those who have not celebrated come up to receive communion.8
In the manuscripts, this antiphon goes under different titles: Ad Eucharistiam9, Ad communicandum, and even Ad corpus Domini frangendum.
Common throughout France, this antiphon is also found in northern Italy, not only in the environs of the territory of the Ambrosian rite (in the Abbey of Nonantola near Modena, in the chapter of Monza, and the Cathedral of Padua), but also in Benevento (under Greek influence for a long time) and even in England (in the troparia of Winchester and Canterbury), where it probably arrived after the Norman Conquest. Nonetheless, its origins clearly seem to lie in the ancient rite of Gaul, whence it passed to the Ambrosian rite.
Musically speaking, there are many indications of Gallican origin: the mode in Re, very common in all the musical pieces that have survived from the ancient rite of Gaul, the very ornate melisma of the final Alleluia on the vowel e (a typically Gallican feature), and finally the use of the pes stratus (on the initial a of Alleluia), a neume made up of a pes followed by an oriscus, which is not found in the Gregorian repertoire.
Listen to the magnificent interpretation of the Venite popule sung by Marie-Claire Billecocq (Le Chant grégorien du soliste, Edition Studio S. M., 1982):
 Translators’ note: In 1771, Archbishop Antoine de Montazet promulgated a new Lyonnese missal based on the neo-Gallican use of Paul, followed in 1775 by a new breviary, over the protests of the canons, who objected to this unprecedented assault on the ancient Lyonnese liturgy.
 Before the obligation was reduced to Easter day alone by the Fourth Lateran Œcumenical Council in 1215, in the famous canon 21 Utriusque sexus.