Ἀνεκαλεῖτο δῆτα ἐν εὐχαῖς τοῦτον, ἀντιβολῶν καὶ ποτνιώμενος φῆναι αὐτῷ ἑαυτὸν ὅστις εἴη καὶ τὴν ἑαυτοῦ δεξιὰν χεῖρα τοῖς προκειμένοις ἐπορέξαι. εὐχομένῳ δὲ ταῦτα καὶ λιπαρῶς ἱκετεύοντι τῷ βασιλεῖ θεοσημεία τις ἐπιφαίνεται παραδοξοτάτη, ἣν τάχα μὲν ἄλλου λέγοντος οὐ ῥᾴδιον ἦν ἀποδέξασθαι, αὐτοῦ δὲ τοῦ νικητοῦ βασιλέως τοῖς τὴν γραφὴν διηγουμένοις ἡμῖν μακροῖς ὕστερον χρόνοις, ὅτε ἠξιώθημεν τῆς αὐτοῦ γνώσεώς τε καὶ ὁμιλίας, ἐξαγγείλαντος ὅρκοις τε πιστωσαμένου τὸν λόγον, τίς ἂν ἀμφιβάλοι μὴ οὐχὶ πιστεῦσαι τῷ διηγήματι; μάλισθ’ ὅτε καὶ ὁ μετὰ ταῦτα χρόνος ἀληθῆ τῷ λόγῳ παρέσχε τὴν μαρτυρίαν. ἀμφὶ μεσημβρινὰς ἡλίου ὥρας, ἤδη τῆς ἡμέρας ἀποκλινούσης, αὐτοῖς ὀφθαλμοῖς ἰδεῖν ἔφη ἐν αὐτῷ οὐρανῷ ὑπερκείμενον τοῦ ἡλίου σταυροῦ τρόπαιον ἐκ φωτὸς συνιστάμενον, γραφήν τε αὐτῷ συνῆφθαι λέγουσαν· “τούτῳ νίκα”. θάμβος δ’ ἐπὶ τῷ θεάματι κρατῆσαι αὐτόν τε καὶ τὸ στρατιωτικὸν ἅπαν, ὃ δὴ στελλομένῳ ποι πορείαν συνείπετό τε καὶ θεωρὸν ἐγίνετο τοῦ θαύματος. καὶ δὴ διαπορεῖν πρὸς ἑαυτὸν ἔλεγε, τί ποτε εἴη τὸ φάσμα. ἐνθυμουμένῳ δ’ αὐτῷ καὶ ἐπὶ πολὺ λογιζομένῳ νὺξ ἐπῄει καταλαβοῦσα. ἔνθα δὴ ὑπνοῦντι αὐτῷ τὸν Χριστὸν τοῦ θεοῦ σὺν τῷ φανέντι κατ’ οὐρανὸν σημείῳ ὀφθῆναί τε καὶ παρακελεύσασθαι, μίμημα ποιησάμενον τοῦ κατ’ οὐρανὸν ὀφθέντος σημείου τούτῳ πρὸς τὰς τῶν πολεμίων συμβολὰς ἀλεξήματι χρῆσθαι. ἅμα δ’ ἡμέρᾳ διαναστὰς τοῖς φίλοις ἐξηγόρευε τὸ ἀπόρρητον. κἄπειτα χρυσοῦ καὶ λίθων πολυτελῶν δημιουργοὺς συγκαλέσας μέσος αὐτὸς καθιζάνει καὶ τοῦ σημείου τὴν εἰκόνα φράζει, ἀπομιμεῖσθαί τε αὐτὴν χρυσῷ καὶ πολυτελέσι λίθοις διεκελεύετο. ὃ δὴ καὶ ἡμᾶς ὀφθαλμοῖς ποτε παραλαβεῖν αὐτὸς βασιλεύς, θεοῦ καὶ τοῦτο χαρισαμένου, ἠξίωσεν. ἦν δὲ τοιῷδε σχήματι κατεσκευασμένον. ὑψηλὸν δόρυ χρυσῷ κατημφιεσμένον κέρας εἶχεν ἐγκάρσιον σταυροῦ σχήματι πεποιημένον, ἄνω δὲ πρὸς ἄκρῳ τοῦ παντὸς στέφανος ἐκ λίθων πολυτελῶν καὶ χρυσοῦ συμπεπλεγμένος κατεστήρικτο, καθ’ οὗ τῆς σωτηρίου ἐπηγορίας τὸ σύμβολον δύο στοιχεῖα τὸ Χριστοῦ παραδηλοῦντα ὄνομα διὰ τῶν πρώτων ὑπεσήμαινον χαρακτήρων, χιαζομένου τοῦ ῥῶ κατὰ τὸ μεσαίτατον· ἃ δὴ καὶ κατὰ τοῦ κράνους φέρειν εἴωθε κἀν τοῖς μετὰ ταῦτα χρόνοις ὁ βασιλεύς. τοῦ δὲ πλαγίου κέρως τοῦ κατὰ τὸ δόρυ πεπαρμένου ὀθόνη τις ἐκκρεμὴς ἀπῃώρητο, βασιλικὸν ὕφασμα ποικιλίᾳ συνημμένων πολυτελῶν λίθων φωτὸς αὐγαῖς ἐξαστραπτόντων καλυπτόμενον σὺν πολλῷ τε καθυφασμένον χρυσῷ, ἀδιήγητόν τι χρῆμα τοῖς ὁρῶσι παρέχον τοῦ κάλλους. τοῦτο μὲν οὖν τὸ φᾶρος τοῦ κέρως ἐξημμένον σύμμετρον μήκους τε καὶ πλάτους περιγραφὴν πελάμβανε· τὸ δ’ ὄρθιον δόρυ, τῆς κάτω ἀρχῆς ἐπὶ πολὺ μηκυνόμενον ἄνω μετέωρον, ὑπὸ τῷ τοῦ σταυροῦ τροπαίῳ πρὸς αὐτοῖς ἄκροις τοῦ διαγραφέντος ὑφάσματος τὴν τοῦ θεοφιλοῦς βασιλέως εἰκόνα χρυσῆν μέχρι στέρνων τῶν τ’ αὐτοῦ παίδων ὁμοίως ἔφερε. τούτῳ μὲν οὖν τῷ σωτηρίῳ σημείῳ πάσης ἀντικειμένης καὶ πολεμίας δυνάμεως μυντηρίῳ διὰ παντὸς ἐχρῆτο βασιλεύς, τῶν τε στρατοπέδων ἁπάντων ἡγεῖσθαι τὰ τούτου ὁμοιώματα προσέταττεν.
(Eusebius, Bios Konstantinou 1.28-31)
This God he began to invoke in prayer, beseeching and imploring him to show him who he was, and to stretch out his right hand to assist him in his plans. As he made these prayers and earnest supplications there appeared to the Emperor a most remarkable divine sign. If someone else had reported it, it would perhaps not be easy to accept; but since the victorious Emperor himself told the story to the present writer a long while after, when I was privileged with his acquaintance and company, and confirmed it with oaths, who could hesitate to believe the account, especially when the time which followed provided evidence for the truth of what he said? About the time of the midday sun, when day was just turning, he said he saw with his own eyes, up in the sky and resting over the sun, a cross-shaped trophy formed from light, and a text attached to it which said, ‘By this conquer’. Amazement at the spectacle seized both him and the whole company of soldiers which was then accompanying him on a campaign he was conducting somewhere, and witnessed the miracle. He was, he said, wondering to himself what the manifestation might mean; then, while he meditated, and thought long and hard, night overtook him. Thereupon, as he slept, the Christ of God appeared to him with the sign which had appeared in the sky, and urged him to make himself a copy of the sign which had appeared in the sky, and to use this as protection against the attacks of the enemy. When day came he arose and recounted the mysterious communication to his friends. Then he summoned goldsmiths and jewellers, sat down among them, and explained the shape of the sign, and gave them instructions about copying it in gold and precious stones. This was something which the Emperor himself once saw fit to let me also set eyes on, God vouchsafing even this. It was constructed to the following design. A tall pole plated with gold had a transverse bar forming the shape of a cross. Up at the extreme top a wreath woven of precious stones and gold had been fastened. On it two letters, intimating by its first characters the name ‘Christ’, formed the monogram of the Saviour’s title, rho being intersected in the middle by chi. These letters the Emperor also used to wear upon his helmet in later times. From the transverse bar, which was bisected by the pole, hung suspended a cloth, an imperial tapestry covered with a pattern of precious stones fastened together, which glittered with shafts of light, and interwoven with much gold, producing an impression of indescribable beauty on those who saw it. This banner then, attached to the bar, was given equal dimensions of length and breadth. But the upright pole, which extended upwards a long way from its lower end, below the trophy of the cross and near the top of the tapestry delineated, carried the golden head-and-shoulders portrait of the Godbeloved Emperor, and likewise of his sons. This saving sign was always used by the Emperor for protection against every opposing and hostile force, and he commanded replicas of it to lead all his armies. (tr. Averil Cameron & Stuart G. Hall)