A phrase applies to various liturgical or devotional acts which have the gesture of tracing two lines intersecting at right angles to indicate symbolically the figure of Christ's cross.
The most common "sign of the cross" is the large cross traced from forehead to breast and from shoulder to shoulder, that Catholics are taught to make upon themselves when they begin their prayers, and the priest makes at the foot of the altar when he commences Mass.
Another sign of the cross is the one made in the air by bishops, priests, and others in blessing persons or material objects. This cross also occurs many times in the liturgy and in nearly all the ritual offices connected with the sacraments and sacramentals.
A third variety is represented by the little cross, generally made with the thumb, which the priest or deacon traces upon the book of the Gospels and then upon his own forehead, lips, and breast at Mass. Or upon the forehead of the infant in Baptism, or upon a person receiving Confirmation or Extreme Unction, etc.
Still another variant of the holy sign may be recognized in the direction of the "Lay Folks Mass Book" (thirteenth century) that the people at the end of the Gospel would trace a cross upon a bench, wall or book and then kiss it. It was prescribed in some early uses that the priest ascending to the altar before the Introit should first draw a cross upon the altar-cloth and then kiss it. Moreover in Spain, it was the prevailing custom, that a man, after making the sign of the cross in the ordinary way kiss his thumb, has a similar origin. The thumb would lay across the forefinger to form an image of the cross to which the lips were devoutly pressed.
Of all the above methods, the marking of a little cross seems to be the most ancient. We have positive evidence from the early Fathers that such a practice was familiar to Christians in the second century. "In all our travels and movements, with all our comings and goings, when putting on our shoes, at bath, at table, in lighting our candles, in lying and sitting down, whatever employment occupies us, we place on our foreheads the sign of the cross" Tertullian (De cor. Mil., iii). On the other hand this must soon have passed into a gesture of benediction, as many quotations from the Fathers in the fourth century show. Thus St. Cyril of Jerusalem in his "Catecheses" (xiii, 36) remarks: "let us then not be ashamed to confess the Crucified. Let the cross be our seal, made with boldness by our fingers on our brow and on every thing; over the bread we eat and the cups we drink, in our comings and goings; before our sleep, when we lie down and when we awake; when we are traveling, and when we are at rest".
The cross was originally traced to Christians using the thumb or finger on their foreheads. This practice is attested by numberless allusions in Patristic literature, and it was clearly associated with certain references in Scripture, notably Ezekiel 9:4; Exodus 17:9-14; and especially Apocalypse 7:3, 9:4 and 14:1. Then there was the custom of marking a cross on objects -- already Tertullian speaks of the Christian woman "signing" her bed ("Ad uxor.", ii, 5) before retiring to rest—and we soon hear of the sign of the cross being traced on the lips (Jerome, "Epitaph. Paulæ") and on the heart (Prudentius, "Cathem.", vi, 129). If the object were more remote, the cross was made in the air towards its location. Thus Epiphanius tells us (Adv. Hær., xxx, 12) of a certain holy man Josephus, who imparted upon a vessel of water the power of overthrowing magical incantations by "making with his finger the seal of the cross over the vessel" while reciting a prayer. Half a century later Sozomen, the church historian (VII, xxvi), describes how Bishop Donatus when attacked by a dragon "made the sign of the cross with his finger in the air and spat upon the monster". This leads to the suggestion that a larger cross was made over the whole body. Perhaps the earliest example comes to us from a Georgian source, possibly the fourth or fifth century. In the life of St. Nino, a woman saint, honored as the Apostle of Georgia, we are told: "began to pray and entreated God for a long time. Then she took her (wooden) cross and with it touched the Queen's head, her feet and her shoulders, making the sign of the cross and straightway she was cured" (Studia Biblica, V, 32).
It appears on the whole that the general introduction of our present larger cross (from brow to breast and from shoulder to shoulder) was an indirect result of the Monophysite controversy. The use of the thumb alone or the single forefinger, from which only a small cross was traced upon the forehead, seems to have given way for symbolic reasons to the use of two fingers (the forefinger and middle finger, or thumb and forefinger) as typifying the two natures and two wills in Jesus Christ. But if two fingers were to be employed, the large cross, in which forehead, breast, etc. were merely touched, suggested itself as the natural gesture. Indeed some large movement of the sort was required to make it perceptible that a man was using two fingers rather than one. At a somewhat later date, throughout the greater part of the East, three fingers, or the thumb and two fingers were displayed, while the ring and little finger were folded back upon the palm.
• The two fingers were held to symbolize the two natures or wills in Christ.
• The extended three fingers denoted the three Persons of the Blessed Trinity.
At the same time the three fingers were so held as to indicate the common abbreviation I X C (Iesous Christos Soter), the forefinger representing the I, the middle finger crossed with the thumb standing for the X and the bent middle finger serving to suggest the C. In Armenia, however, the sign of the cross made with two fingers is still retained to the present day. Much of this symbolism passed to the West, at a later date.
It seems probable that the prevalence of the larger cross is due to an instruction of Leo IV in the middle of the ninth century. "Sign the chalice and the host", he wrote, "with a right cross and not with circles or with a varying of the fingers, but with two fingers stretched out and the thumb hidden within them, by which the Trinity is symbolized. Take heed to make this sign rightly, for otherwise you bless nothing" (see Georgi, "Liturg. Rom. Pont.", III, 37). Although this, of course, applies primarily to the position of the hand in blessing with the sign of the cross; it seems to have been adapted popularly to the making of the sign of the cross upon oneself. Aelfric (about 1000) probably had this in mind when he tells his hearers in one of his sermons: "A man may wave about wonderfully with his hands without creating any blessing unless he makes the sign of the cross. If he does the fiend will soon be frightened on account of the victorious token. With three fingers one must bless himself for the Holy Trinity" (Thorpe, "The Homilies of the Anglo-Saxon Church" I, 462). Fifty years earlier Anglo-Saxon Christians were exhorted to "bless all their bodies seven times with Christ's rood token" (Blicking Hom., 47), which seems to assume this large cross. Bede in his letter to Bishop Egbert advises him to remind his flock "that frequent diligence be employed upon themselves to make the sign of our Lord's cross", though here we have no idea what kind of cross was to be made. On the other hand when we read in the so-called "Prayer Book of King Henry" (eleventh century) a direction in the morning prayers to make the holy Cross on "the four sides of the body", there is good reason to suppose that the large sign with which we are now familiar with is meant.
At this period the manner of making it in the West seems to have been identical with that followed in the East, i.e. only three fingers were used, and the hand traveled from the right shoulder to the left. The point, it must be confessed, is not entirely clear for Thalhofer (Liturgik, I, 633) inclines to agree with the opinion found in the passages of Belethus (xxxix), Sicardus (III, iv), Innocent III (De myst. Alt., II, xlvi), and Durandus (V, ii, 13), which are usually appealed to in proof of this, that the small cross made upon the forehead or external objects, in which the hand moves naturally from right to left was meant, and not the big cross made from shoulder to shoulder. Still, a rubric in a manuscript copy of the York Missal clearly requires the priest when signing himself with the paten to touch the left shoulder after the right. Moreover it is clear from many pictures and sculptures that in the twelfth and thirteenth centuries the Greek practice of extending only three fingers was adhered to by many Latin Christians. Thus the compiler of the Ancren Riwle (about 1200) directs his nuns at "Deus in adjutorium" to make a little cross from above the forehead down to the breast with three fingers". However there can be little doubt that long before the close of the Middle Ages the large sign of the cross was more commonly made in the West with the open hand; and that the bar of the cross was traced from left to right. In the "Memory of our Lady" (p. 80) the Bridgettine Nuns of Sion have a mystical reason given to them for the practice: "And when you bless yourself with the sign of the holy cross, you chase away the fiend with all his deceptions. For, as Chrysostome says, wherever the fiends see the sign of the cross, they fly away, dreading it as a staff that they are beaten with. And in your blessing you begin with your hand at the head downward, and then to the left side believing that our Lord Jesus Christ:
• came down from the Father
• to the earth by His holy Incarnation
• descending into hell, by his bitter Passion
• ascending to His Father's right side by his glorious Ascension".
The manual act of tracing the cross with the hand or the thumb has always been accompanied by a prayer. The formula, however, has varied greatly. In the earlier ages we have evidence for such invocations as:
1. "The sign of Christ"
2. "The seal of the living God"
3. "In the name of Jesus"
4. "In the name of Jesus of Nazareth"
5. "In the name of the Holy Trinity"
6. "In the name of the Father and of the Son and of the Holy Spirit"
7. "Our help is in the name of the Lord"
8. "O God come to my assistance"
Members of the Greek Orthodox Church when blessing themselves with three fingers, commonly use the invocation:
• "Holy God, Holy strong One, Holy Immortal One, Have mercy on us"
These words can be found in their Greek form by the Western Church in the Office for Good Friday.
From the earliest period it has been employed for all exorcisms and conjurations as a weapon against the spirits of darkness, and it takes its place consistently in the ritual of the sacraments and in every form of blessing and consecration. A famous problem arose over the making of the sign of the cross repeatedly over the Host and Chalice after the words of institution have been spoken in the Mass. At the time these crosses were introduced, the clergy and faithful were not clear as to the precise moment the transubstantiation of the elements was effected. They were satisfied that it was the result of the whole of the consecratory prayer which we call the Canon, without determining the exact words which were operative.* Hence the signs of the cross continued till the end of the Canon as they may be regarded as referring back to a consecration which was still conceived as incomplete. The process is the reverse of that by which in the Greek Church at the "Great Entrance" the highest marks of honor are paid to the simple elements of bread and wine in anticipation of the consecration which they are to receive shortly.
* Today we are now content to know that the Precious Blood is consecrated by the whole word spoken over the chalice.