(In the mid-seventeenth century the English “vulgar” took on a new definition of “coarse,” but it wouldn’t be until this “coarse/unrefined” definition would become more common in the 20th century that referring to the Vulgar Era would cease.)(1715).As for the actual abbreviation, CE (Common Era) has been claimed to have been used as early as 1831, though I couldn’t find specifically in what work it is supposed to have appeared in.
When that didn’t work, Christians began to be killed in various brutal ways including occasionally being torn apart by animals for the amusement of the masses (Damnatio ad bestias).
This method of convincing people to worship the Roman gods ended up being an amazing failure and the persecution appears to have only continued after AD 305 in the Eastern half of the empire under Galerius and Maximinus.
When "Christian Era" is used, it's still clear what epoch is being referred to (i.e.
the Western one) without having to have some special knowledge about what "anno domini" means or who Christ is.
Previous to this, he had purportedly only advocated banning Christians from such things as the military and ruling body in hopes that would appease the gods.