Ashoka was the Indian Constantine,

or more correctly,Constantine was the Roman Ashoka.

But who was Ashoka?

Diodotus   I   may have been Ashoka. Buddhists claim that King Ashoka (273-232 BCE)….., citing his pillars and rock edicts as evidence of this activity. In fact nowhere in these pillars and edicts is Buddhism ever mentioned, though he does mention dharma pretty often.[As a skeptic, I believe Ashoka may never have existed. Certainly not under that name. But for the sake of argument let us suppose the person we now know as Ashoka  had existed].. For details,

But as John S. Strong says in The Legend of King Asoka, “Precisely what Ashoka meant by Dharma has been the subject of much debate. In Buddhist circles, the word means the Buddha’s Teachings—his doctrine—...

More generally, however,Dharma can be translated as law, duty, or righteousness, and as such it has many overtones in Indian religion.

However he intended it, in his edicts, Ashoka seems to have been obsessed with Dharma. The Ashokan state was to be governed according to Dharma. The people were to followDharma. Wars of aggression were to be replaced by peaceful conquests of Dharma. Special royal ministers were charged with the propagation of Dharma. True delight in this world came only with delight in Dharma, and the old royal pleasure-tours and hunts were replaced by Dharma-pilgrimages.

Map of Mauryan Empire at its height under Ashoka.

"From these and other indications, we may say that Dharma seems to have meant for Ashoka a moral polity of active social concern, religious tolerance, ecological awareness, the observance of common ethical precepts,..."