Britannia Prima

Following the Roman conquest of Britain, it was administered as a single province from Camulodunum (Colchester) and then Londinium (London) until the Severan Reforms following the revolt of its governor Clodius Albinus.

These divided the territory into Upper and Lower Britain (Britannia Superior and Inferior), whose respective capitals were at Londinium and Eboracum (York).

At some point after the territory was retaken by Constantius Chlorus in AD 296, the Diocese of the Britains (with its vicar at Londinium) was established and made a part of the Prefecture of Gaul.

[6] Modern scholars disregard this gloss but generally agree in placing Britannia Prima in Wales, Cornwall (Cornubia), and the area connecting them.

Ammianus records that in the year 369 Count Theodosius established or refounded the province of Valentia (further attested in the List of Offices) from lands recaptured from "the enemy".

Roman Britain around AD 410 , without speculative provincial borders.
The traditional arrangement of the late Roman provinces after Camden , [ 2 ] placing Prima along England's southern coast. On the basis of modern archaeology, the province at least reached as far north as Corinium .
Another possible arrangement of the late Roman provinces, with Prima in Wales and Cornwall
Inscription of Lucius Septimius