It is generally agreed that St. Christopher did live in the late third and early fourth century. He was taken prisoner in a war with the Romans in North Africa, in present day Libya. He was forced to travel a great distance back to Rome and was assigned as a Roman army officer during the reign of Emperor Diocletian.
A terrible persecution of Christians took place at the command of this emperor. It was one of Diocletian's own guards who refused to participate in the persecution and proclaimed himself a Christian. This guard was St. George. The emperor ordered that St. George be tortured and killed. St. Christopher, who was a soldier there at the time, watched the torture and killing of St. George, and shortly after declared himself also to be a Christian, an admission which caused him to be put to death.
It is thought that his name originally was Reprobus, but was changed to Christopher, meaning "Christ-bearer," because of the story which tells of a child approaching St. Christopher by a river, who asked to be helped across. St. Christopher obliged. However, as he entered midstream, the river rose and the child's weight grew and became extremely heavy. It was only by great exertion that St. Christopher safely delivered the child to the other side. When St. Christopher asked the child why He was so heavy, the child explained that He was the Christ and when St. Christopher carried Him, he also carried the weight of the whole world on his shoulders. The child then vanished.
Although St. Christopher is no longer included in the Church's general liturgical calendar, he is commemorated on July 25th in those places dedicated to him, as well as by those who bear his name. He continues to be invoked as a patron for travellers, and is counted as one of the Fourteen Holy Helpers, a group of saints known for their particularly powerful intercession.
This Collect is from the Sarum Missal:
Concede, quaesumus, omnipotens et misericors Deus, ut qui beati Christophori martyris tui memoriam agimus, ejus piis meritis et intercessionibus a morte perpetua, subitanea peste, fame, timore, paupertate, et ab omnibus insidiis inimicorum liberemur in terris; per te Jesu Christe, salvator mundi, rex gloriae, quem idem Christophorus meruit in suis humeris portare. Qui vivis et regnas cum Deo Patre, in unitate Spiritus sancti Deus: per omnia secula seculorum. Amen.
[Grant, we ask, almighty and merciful God, that we who keep the memory of Thy blessed martyr Christopher, by his pious merits and intercession may be delivered on earth from perpetual death, sudden plague, famine, fear, poverty, and from all the snares of our enemies; through Thee, Jesus Christ, Savior of the world, and King of glory, whom the same Christopher merited to bear upon his shoulders. Who livest with the Father, in the unity of the Holy Spirit, one God, for ever and ever. Amen.]
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Painting: "St. Christopher Carrying the Infant Jesus"
by Edmond Lechevallier-Chevignard (1825-1902)