That Hadrian and not Severus (by whose name it is often called) was the builder of the Wall as well as of the adjoining fortresses is proved by his inscriptions being found not only in them, but in the "mile-castles" [see C.I.L. vii. 660-663]. Out of the 14 known British inscriptions of this Emperor, 8 are on the Wall; out of the 57 of Severus, 3 only.
Hadrian divided the Province of Britain [see p. 142] into "Upper" and "Lower"; but by what boundary is wholly conjectural. All we know is that Dion Cassius [Xiph. lv.] places Chester and Caerleon in the former and York in the latter. The boundary may thus have been the line from Mersey to Humber; "Upper" meaning "nearer to Rome."
Neilson, 'Per Lineam Valli,' p.I.
See further pp. 203-212.