The great event in the religious history of Constantine took place in 312. He was marching from France to Italy against Maxentius. The approaching contest was one of immense moment. It was likely either to be his ruin or to raise him to the highest pinnacle of power. He was in deep thought. It was known that Maxentius was making great preparations for the struggle, by enlarging his army, and by scrupulously attending to all the customary ceremonies of paganism. He consulted with great pains the heathen oracles, and relied for success on the agency of supernatural powers.
Constantine, though a wise and virtuous heathen, was a heathen still. He knew what he had to give battle to; and while considering to what god he should betake himself for protection and success, he thought on the ways of his father, the Emperor of the West. He remembered that he prayed to the God of the Christians and had always been prosperous, while the emperors who persecuted the Christians had been visited with divine justice. He resolved therefore to forsake the service of idols, and to ask the aid of the one true God in heaven. He prayed that God would make Himself known to him, and that He would make him victorious over Maxentius, notwithstanding all his magical arts and superstitious rites.
While engaged in such thoughts, Constantine imagined that he saw, soon after mid-day, some extra-ordinary appearance in the heavens. It assumed the sign of a glittering cross, and above it the inscription, "By This Conquer." The Emperor and the whole army, who were witnesses of this wonderful sight, stood awestruck. But while the Emperor was gravely meditating on what the vision could signify, night came on, and he fell asleep. He dreamed that the Savior appeared to him, bearing in His hand the same sign which he had seen in the heavens, and directed him to cause a banner to be made after the same pattern, and to use it as his standard in war, assuring him that while he did so he would be victorious. Constantine, on awakening, described what had been shown to him while asleep, and resolved to adopt the sign of the cross as his imperial standard.