Northwest Europe, Britain (Britannia), 5C ENGLAND, Roman Period (43-410): Diocletian Tetrarchy (293-305)

Diocletian doubled the number of provinces from 50 to 100, organising the provinces into twelve dioceses, with each of the bigger units being controlled by a vicarius; the diocese of the Britons (Britannia) being called Britanniae. In c.312 this was split into four provinces (Verona List), the details are not known exactly but one version has Britannia Prima covering Wales and the west country with its capital at Corinium Dobunnorum/Cirencester; Flavia Caesariensis covering the Midlands and Lincolnshire with its capital at Ratae/Leicester and possibly at Lindum/Lincoln; Britannia Secunda north of this up to and including Hadrian’s Wall with its capital at Eboracum/York; and Maxima Caesariensis covering the southeast and East Anglia (its coast was the Saxon Shore), with its capital and that of the diocese at Londinium/London. 

A fifth province, Valencia, is mentioned as either a new province or the renaming of land regained in 369. Its existence is debated and hypotheses for its location include the area between the Antonine Wall and Hadrian’s Wall, the area south of Hadrian’s Wall and Wales. 

Constantine-I eventually emerged victorious in the civil wars against Maxentius (West; c.34; r.307-312) and Licinius (East) by 324 to become the sole ruler of the Roman Empire. After his death in 337, his three sons Constantine II (24; r.337-340), Constans (c.27; r.337-350) and Constantius II (44; r.337-361) took charge respectively of the prefectures of Galliae (west, the dioceses of Britannia, Gaul, Hispania and Vienne), Italia (central, the dioceses of Africa, Dacia, Italy, Pannonia and Macedonia) and Orientis (east, the dioceses of Asia, Egypt, Oriens/Levant, Pontus and Thrace). 

 In 343 Constans visited Britain, linked by some to an issue with scouts (areani) of the northern frontier. In 350 Constans was usurped by the commander ²⁶Flavius Magnus Magnentius (50; fl.350-353) and Britain sent troops to Gaul to assist him in his claim. In 353 Constantius II defeated Magnentius and sent Paulus Catena (350s, d. 361/2), a senior Roman public official, to arrest certain supporters of Magnentius. In 355, Constantius II made the future emperor Julian (31/32; r.360-363) caesar of Galliae.