The earliest use I find in Latin is in the Historiarum Adversum Paganos Libri VII, Seven Books of Histories Against the Pagans" (or the Hormesta), by Orosius, who wrote about 418 AD. There is an interesting gloss on this, as to put it in everyday speech [Seven Books of History against the Pagans, Liverpool University Press, 2010, p.412], which implies that Romania was a term more common in sp