The following excerpt is taken from Bert Ghezzi’s book Sign of the Cross: Recovering the Power of the Ancient Prayer (Word on Fire Publishing).

During the Reformation of the sixteenth century, some Christians repudiated the sign of the cross because they judged it to be superstitious. But Martin Luther himself did not abandon it and recommended the practice in his Small Catechism in an appendix on family prayer. Today, athletes who sign themselves for good luck at sporting events reinforce the opinion that it is a superstition. But basketball players at the foul line were not the first to abuse the gesture by ascribing to it magical powers that could be turned to dubious personal advantage. As early as the sixth century, St. Caesarius (470–542), the bishop of Arles and one of Christianity’s first best-selling authors, rebuked Christians who signed themselves while on their way to steal or commit adultery.  

But no trace of superstition or magic marred the sign of the cross in its origins. While no direct evidence exists, it seems clear from circumstances that the holy gesture had its roots as a prayer in apostolic times. Fourth-century Father of the Church St. Basil (329–379) said that the Apostles “taught us to mark with the sign of the cross those who put their hope in the Lord”—that is, those who presented themselves for Baptism. 

So early Christians probably learned to make the sign of the cross at their Baptism when the celebrant marked them with it to claim them for Christ. There is some evidence for this in Scripture. For example, St. Paul reminded the Ephesians that they received the sign at Baptism when he said: “You have been stamped with the seal of the Holy Spirit of the Promise” (1 Cor. 1:13). And Paul may have been speaking of his being signed with the cross at Baptism when he told the Galatians that “I carry branded on my body the marks of Jesus” (Gal. 6:17). I will say more about this later, but for now I merely want to show you that the sign of the cross originated among people who were not far removed from Christ himself. 

Early Christians used the thumb or index finger to trace a little cross on their foreheads. They associated the practice with references in Ezekiel 9:7 and Revelation 7:3, 9:4, and 14:1, all of which describe believers bearing God’s seal on their foreheads. That mark was a cross—the Greek letter tau—that was written as a T and stood for the name of God. Origen (c. 185–c. 253), a third-century theologian and spiritual writer, commented on the Ezekiel passage by quoting a writer who said: 

The shape of the letter tau presented a resemblance to the figure of the cross and this represented a prophecy of the sign that Christians make on their foreheads. For all the faithful make this sign when they undertake any activity, especially prayer or reading Holy Scripture. 

So by the third century, Christians frequently marked their foreheads with the cross. They also traced the little sign on their lips and breasts, as we still do today when the Gospel is announced at Mass. And they made the sign in the air as a blessing over persons and things. Tertullian, for example, told of a woman who signed her bed, and St. Cyril of Jerusalem described Christians tracing the cross “over the bread we eat and the cups we drink.” Using the sign of the cross as a blessing may have prompted some Christians to make the larger sign that we know today, but that practice did not come into common use until later on. 

Opposition to the Monophysite heresy in the seventh and eight centuries may have contributed to popularizing the larger sign. To summarily refute these heretics, who held that Christ had only one divine nature instead of two natures, one human and one divine, Christians in the East began to sign themselves with two fingers or with the thumb and forefinger. They had to trace a larger sign over their breasts so that their use of two fingers to defend the truth would be visible to all. Imagine the duel that occurred when a Christian encountered a Monophysite. The Christian would conspicuously make a large sign with two fingers and hurry to the other side of the street. The Monophysite would respond with a large sign made with his index finger and walk off in a huff. The idea of that scene may make us smile, but in those days ordinary folks’ tempers flared over theological issues. 

By the ninth century, Christians in the East were making the larger gesture with thumb and two fingers displayed, symbolizing the Trinity, and with the ring and little finger folded back, symbolizing Christ’s two natures. In the middle of the eighth century, at a time when emperors had a lot to say about ecclesiastical matters, Byzantine emperor Leo IV decreed that all blessings should be made with a large right cross—that is, with the horizontal gesture moving from right to left. Although this proclamation applied to blessings, it was popularly adapted to the gesture of signing oneself. The emperor’s directive established the large sign as the common practice in the East. Christians of the Eastern Churches signed themselves with two fingers and thumb extended, touching their forehead and moving to their breast, then crossing their shoulders from right to left. 

How Western Christians came to adopt the larger sign of the cross is less clear. Apparently after the ninth century some Western Christians imitated the practice of the Eastern Church and signed themselves with a large right cross. But at the same time others in the West had begun to trace the large cross over their breasts moving their hand from the left shoulder to the right shoulder. 

Innocent III (1160–1216), who was pope at the beginning of the thirteenth century, directed that Christians sign themselves with two fingers and thumb extended. He allowed that some make a right cross and others a left cross, indicating no preference for either approach. But before the end of the Middle Ages, Western Christians showed a preference for signing themselves with a large left cross. For example, the Myroure of Our Ladye, a late-fifteenth-century document, taught the Brigittine Sisters of Syon Abbey in Middlesex, England, to cross themselves from left to right. It explained that the movement from forehead to breast meant that Christ came down from heaven to earth in his Incarnation, and the movement from the left to right shoulder indicated that Christ at his death descended into hell and then ascended to heaven to sit at the Father’s right hand. 

By the end of the Middle Ages, probably under the extensive influence of Benedictine monasteries, where the practice was to make a large left cross with an open hand, most Western Christians were making the sign of the cross as we do today. 

In every age Christians commonly, but not indispensably, accompanied the act of making the sign with words of prayer. But the prayers varied greatly. In the earlier period, they used invocations like “The sign of Christ,” “The seal of the living God,” and “In the name of Jesus.” In later ages, they prayed, “In the name of Jesus of Nazareth,” “In the name of the Holy Trinity,” and “In the name of the Father, and of the Son, and of the Holy Spirit,” the latter being the most common prayer that we use today. Christians have also used formulas suggested by the liturgy, like “O God come to my assistance” and “Our help is in the name of the Lord.” This diversity of words accompanying the sign should encourage you to pray spontaneously when you cross yourself, a practice that I recommend in later chapters. 

Twenty-first-century Christians have inherited a diversity of ways to make the sign. Today you will see people marking themselves with large left crosses or large right crosses, with open hand or with two fingers and thumb extended; tracing little crosses on their foreheads, lips, and breasts with one finger, two fingers, or with thumb and forefinger. You may see a Latino youth make a large left cross and then kiss a little cross made with thumb and forefinger, a practice rooted in the ancient past. You will see clergy in liturgical settings and laypeople in ordinary situations blessing persons and objects with two fingers and a thumb or an open hand. But no matter how they do it, large or small, with one finger, two, three, or an open hand, all who sign themselves with faith are opening themselves to the Lord.