Tertullian: At every forward step and movement, at every going in and out, when we put on our our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign (The Chaplet 3 [A.D. 211]).
Acts of Xanthippe and Polyxena: And Paul perceived her prayer, and made the sign of the cross, and for several days the people entered unhindered, and as many as had sick and vexed by unclean spirits brought them, and all were healed (14 [A.D. 270]).
St. Cyril of Jerusalem: Let us, therefore, not be ashamed of the Cross of Christ; but though another hide it, do thou openly seal it upon thy forehead, that the devils may behold the royal sign and flee trembling far away. Make then this sign at eating and drinking, at sitting, at lying down, at rising up, at speaking, at walking: in a word, at every act. For He who was here crucified is in heaven above (Catechetical Lecture 4:14 [A.D. 350]).
St. Athanasius: Them he quickly heard, though he had not given a thought to the demons, and coming to the door he besought them to depart and not to be afraid, ‘for thus,’ said he, ‘the demons make their seeming onslaughts against those who are cowardly. Sign yourselves therefore with the cross, and depart boldly, and let these make sport for themselves.’ So they departed fortified with the sign of the Cross (Life of St. Anthony 13 [A.D. 356-362]).
But we by the mention of Christ crucified put all demons to flight, whom you fear as if they were gods. Where the sign of the Cross is, magic is weak and witchcraft has no strength (ibid 78).
St. Ephraim the Syrian: With the sign of the living cross, seal all thy doings, my son. Go not forth from the door of thy house till thou hast signed the cross. Whether in eating or in drinking, whether in sleeping or in waking, whether in thy house or on the road, or again in the season of leisure, neglect not this sign; for there is no guardian like it. It shall be unto thee as a wall, in the forefront of all thy doings. And teach this to thy children, that heedfully they be conformed to it (On Admonition and Repentance 17 [A.D. 363]).
St. Gregory of Nyssa: For if the confession of the revered and precious Names of the Holy Trinity is useless, and the customs of the Church unprofitable, and if among these customs is the sign of the cross, prayer, baptism, confession of sins, a ready zeal to keep the commandment, right ordering of character, sobriety of life, regard to justice, the effort not to be excited by passion, or enslaved by pleasure, or to fall short in moral excellence (Against Eunomius11:5 [A.D. 382]).
St. John Chrysostom: When therefore thou signest thyself, think of the purpose of the cross, and quench anger, and all the other passions. When thou signest thyself, fill thy forehead with all courage, make thy soul free (Homily 54 0n Matthew’s Gospel 7 [A.D. 390]).
Origen: This (the letter Tau) bears a resemblance to the figure of the cross; and this prophecy (Ezekiel 9:4) is said to regard the sign made by Christians on the forehead, which all believers make whatsoever work they begin upon, and especially at the beginning of prayers, or of holy reading (Homilies on Ezekial 9 [circa A.D. 392]).
Tyrannius Rufinus: At this point, as the custom is at the close of the Creed, we touch the forehead of this flesh with the sign of the cross (Apology 1:5 [A.D. 400]).
St. Jerome: In every act we do, in every step we take, let our hand trace the Lord’s cross. (Letter 22:37 [A.D. 384]).
And although she signed her mouth and her breast with the sign of the cross, and endeavored thus to alleviate a mother’s grief; her feelings overpowered her and her maternal instincts were too much for her confiding mind(Letter 108:21 [A.D. 404]).
Raising her finger also to her mouth she made the sign of the cross upon her lips. (Letter 108:29 [A.D. 404]).
They will suffice to warn you that you must shut the door of your breast and fortify your brow by often making the sign of the cross (Letter 130:9 [A.D. 414]).
Apostolic Constitutions: Let the high priest, therefore, together with the priests, pray by himself; and let him put on his shining garment, and stand at the altar, and make the sign of the cross upon his forehead with his hand, and say: The grace of Almighty God, and the love of our Lord Jesus Christ, and the fellowship of the Holy Ghost, be with you all (8:7 [A.D. 400]).
St. Augustine: What is the sign (or seal) of Christ, but the cross of Christ? Which sign, unless it be applied, whether to the foreheads of believers, or to the water itself whereby they are regenerated, or to the oil wherewith they are anointed with chrism, or to the sacrifice by which they are fed, none of these things is rightly performed. How then can it be, that by that which the wicked do no good thing is signified, when by the cross of Christ, which the wicked made, every good thing is signified to us in the celebration of His sacraments (Tractates on the Gospel of John 118:5 [circa A.D. 407]).
Paulus Orosius: Theodosius narrowing himself without friends, but that he was surrounded by enemies, with his body prostrate on the earth, but his mind fixed on heaven, prayed alone to Christ alone, who is able to do all things. Having spent a sleepless night in uninterrupted prayer . . . he confidently, though alone, seized his weapons, conscious that he was not only to be protected by the sign of the cross, but thereby even to be victorious; fortifying himself with that sign, he gave the signal for battle” (History Against the Pagans 1:7 [A.D. 417]).