The hymn was first sung in the procession (November 19, 569) when a relic of the True Cross, sent by the Byzantine Emperor Justin II from the East at the request of St. Radegunda, was carried in great pomp from Tours to her monastery of Saint-Croix at Poitiers. Its original processional use is commemorated in the Roman Missal on Good Friday, when the Blessed Sacrament is carried in procession from the Repository to the High Altar. Its principal use however, is in the Divine Office, the Roman Breviary assigning it to Vespers from the Saturday before Passion Sunday daily to Maundy Thursday, and to Vespers of feast of the Exaltation of the Holy Cross (September 14), and in pre-Vatican II breviary also for the feast of the Finding (May 3), and of the Triumph of the Holy Cross (July 16).
Originally the hymn comprised eight stanzas. In the tenth century, stanzas 7 and 8 were gradually replaced by new ones ("O crux ave, spes unica", and the doxology, "Te summa Deus trinitas"), although they were still retained in some places.
"Vexilla" has been interpreted symbolically to represent baptism, the Eucharist, and the other sacraments. Clichtoveus explains that as vexilla are the military standards of kings and princes, so the vexilla of Christ are the cross, the scourge, the lance, and the other instruments of the Passion "with which He fought against the old enemy and cast forth the prince of this world". Johann Wilhelm Kayser dissents from both, and shows that the vexillum is the cross which (instead of the eagle) surmounted, under Constantine, the old Roman cavalry standard. This standard became in Christian hands a square piece of cloth hanging from a bar placed across a gilt pole, and having embroidered on it Christian symbols instead of the old Roman devices.
The splendour and triumph suggested by the first stanza can be appreciated fully only by recalling the occasion when the hymn was first sung--the triumphant procession from the walls of Poitiers to the monastery with bishops and princes in attendance and with all the pomp and pageantry of a great ecclesiastical function. "And still, after thirteen centuries, how great is our emotion as these imperishable accents come to our ears!" (Pimont). There are about forty translations into English verse.
References in later works
Gounod took a very plain melody based on the chant as the subject of his "March to Calvary" in the "Redemption", in which the chorus sings the text at first very slowly and then, after an interval, fortissimo.
Franz Liszt wrote a piece for solo piano, Vexilla regis prodeunt, S185, and the pentatonal theme is used throughout Via Crucis (The 14 stations of the Cross), S53.
Gustav Holst used both the words and the plainchant melody of Vexilla regis in his Hymn of Jesus (1917).