The Ecclesiastical History of Sozomen 5Constantine commands the Sign of the Cross to be carried before him in Battle; an Extraordinary Narrative about the Bearers of the Sign of the Cross.

The emperor, amazed at the prophecies concerning Christ which were expounded to him by the priests, sent for some skillful artisans, and commanded them to remodel the standard called by the Romans Labarum, to convert it into a representation of the cross, and to adorn it with gold and precious stones. This warlike trophy was valued beyond all others; for it was always wont to be carried before the emperor, and was worshiped by the soldiery. I think that Constantine changed the most honorable symbol of the Roman power into the sign of Christ, chiefly that by the habit of having it always in view, and of worshiping it, the soldiers might be induced to abandon their ancient forms of superstition, and to recognize the true God, whom the emperor worshiped, as their leader and their help in battle; for this symbol was always borne in front of his own troops, and was, at the command of the emperor, carried among the phalanxes in the thickest of the fight by an illustrious band of spearmen, of whom each one in turn took the standard upon his shoulders, and paraded it through the ranks. It is said that on one occasion, on an unexpected movement of the hostile forces, the man who held the standard in terror, placed it in the hands of another, and secretly fled from the battle. When he got beyond the reach of the enemy's weapons, he suddenly received a wound and fell, while the man who had stood by the divine symbol remained unhurt, although many weapons were aimed at him; for the missiles of the enemy, marvelously directed by divine agency, lighted upon the standard, and the bearer thereof, although in the midst of danger, was preserved.

It is also asserted that no soldier who bore this standard in battle ever fell, through any dark calamity, such as is wont to happen to the soldiery in war, or was wounded, or taken prisoner.