"He said, moreover, that he doubted within himself what the import of this apparition could be. And while he continued to ponder and reason on its meaning, night suddenly came on; then in his sleep the Christ of God appeared to him with the same sign which he had seen in the heavens, and commanded him to make a likeness of that sign which he had seen in the heavens, and to use it as a safeguard in all engagements with his enemies. At dawn of day he arose, and communicated the marvel to his friends..."
‒ Eusebius (263 A.D. - 339 A.D)
Who is Eusebius referring to in his account? Why is the conversion of this individual important in relation to the Roman Empire? How did it change the empire from that point forward?