The title of this chapter is meant to echo the famous message Samuel F. B. Morse sent from Washington to Baltimore on May 24, 1844, to inaugurate his new service, the telegraph, “What hath God wrought?” I have substituted Constantine for God in Morse’s phrase not to commit blasphemy, but for two more immediate purposes. The first, and most obvious, is to call to mind the events of this reign of more than thirty years, one of the most momentous in Western history; the second is to look at one moment in that long career as a way of understanding a long-standing scholarly controversy over the motives and intentions of the first Christian emperor.