ὁ δὲ Σεβῆρος … διοικήσας δὲ τὰ κατὰ Βρετανίαν καì
διελὼν ἐς δύο ἡγεμονίας τὴν τοῦ ἔθνους ἐξουσίαν….
Thus Herodian (III, 8, 1–2), referring to the time after the Battle of Lugdunum in 197. It is a sign of our imperfect knowledge of the history of Roman Britain that the character of this division, its purpose and even its date, are all matters of doubt. Not only is there no evidence to confirm Herodian's statement until a considerably later period, but there are several contrary indications which suggest that his date, at least, is wrong. Such a conflict of ancient testimony leads, not surprisingly, to differences in modern authorities. It is not necessary, however, for it to lead to such a confusing picture as they now seem to present. Ritterling and E. Birley drew attention to the problem, and S. N. Miller set out all the evidence in the Cambridge Ancient History. It therefore seems unfortunate that eminent authorities in more recent works continue to accept Herodian's date, or, more rarely, offer an alternative, without any warning that they are handling dubious or hypothetical material. My aim in this paper is, therefore, partly one of clarification and restatement. But I also wish to draw attention to a small addition to the evidence on the subject, and to treat the whole problem anew in the light of recent additions to our knowledge of Roman Britain in Severan times. Until a fortunate epigraphic discovery solves the problem for us, all such discussions are bound to be inconclusive; but while we wait for a British Julius Cerealis, an interim statement may crave a hearing.