The great difficulty in the way of this explanation is that Pelagius is always described as a Briton, not as an Irishman or Scotchman. As a fact, however, at that time Scotland was included under the name of Britain; but whether it was or not, St. Jerome does not say that Pelagius was a Scot, but that he was of Scottish race, which is altogether different, and which is perfectly compatible with his British birth. The authorities indeed in favour of his being in some sense a Briton, are quite conclusive. St. Augustine, his greatest opponent, frequently speaks of Pelagius as a Briton.[55] St. Prosper of Aquitaine, who continued to assail him after the death of Augustine, describes him as a 'British snake;'[56] and in another passage he speaks of him as nurtured amongst the 'sea-girt Britons.' Elsewhere he describes Britain as the native land (_patria_) of the Pelagian heresy, which can be true only in so far as it produced Pelagius himself. Marius Mercator says,[57] like St. Jerome, that the first author of the heresy was the Syrian Rufinus, but being too cunning to expose himself to danger, he propagated his doctrines through the agency of the 'British monk' Pelagius. Everything, therefore, points to the fact that Pelagius was of British birth, but of Scottish origin. St. Jerome's expression--_per Albinum canem_--seems to point to a Scot of Alba rather than of Erin; but in any case the Scots of both countries, especially at this early period (A.D. 420), were of the same race. If Britain be taken to include Scotland, as it certainly did at that period, then 'de vicinia Brittanorum' must refer to Ireland; but it should be borne in mind that St. Jerome speaks not of Britain, but of the Britons--quite another thing.