Every once in a while my eye catches what I think are outdated or non-standard forms of Latin names of Roman emperors (and empresses) and wonder if people are writing them like this from habit or reading old references or just making them up as they go along. But the grand revelation I just realized is that there is no real rule at play, it's all arbitrary and no one way right or wrong. I used to think that the rule (sez who?) was that Latin names were anglicized when the root of the name was still in use. That explains why in English we turn Constantinus into "Constantine" and say Hadrian instead of Hadrianus. But this rule breaks down quickly because you never see "Gallien" rather than Galilenus and you absolutely never see Claudius turned into Claude. Extreme anglification would result in some comical transformations like "Antony Pius", "Commode" and, heh, "Tit". Still I see people often still writing names like Domitianus or Maximianus when those suffixes have gone out of style by World War II at least. Altogether we sit on the conservative side between the German purists, who rarely change the old form names, and the Romance languages which feel free to make new names altogether. Nero becomes Nerone in Italian, Aemilian turns to Émilien in French and the absolutely egregious Spanish conversion from Iohannes to "Juan"! Pet peeves anyone?