thumb|right|300px|[[Roman Britain around AD 410, without speculative provincial borders.]]

Britannia Secunda or Britannia II (Latin for "Second Britain") was one of the provinces of the Diocese of "the Britains" created during the Diocletian Reforms at the end of the 3rd century. It was probably created after the defeat of the usurper Allectus by Constantius Chlorus in AD 296 and was mentioned in the Verona List of the Roman provinces. Its position and capital remain uncertain, although it probably lay further from Rome than Britannia I. At present, most scholars place Britannia II in Yorkshire and northern England. If so, its capital would have been Eboracum (York).

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left|200px|thumb|The traditional arrangement of the late Roman provinces after [[William Camden|Camden, placing Secunda in Wales. On the basis of modern archaeology, Prima at least reached as far north as Corinium.]]

left|200px|thumb|Another possible arrangement of the late Roman provinces, with Secunda in northern England

History

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 Britannia Superior and Britannia Inferior, whose respective capitals were at Londinium and Eboracum. During the first phases of the Diocletian Reforms, Britain was under the control of the Allectus's Britannic Empire as part of the Carausian Revolt. 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 formed and made a part of Prefecture of Gaul. The Britains were divided among three, four, or five provinces,

The placement and capitals of these late British provinces are uncertain, although the Notitia Dignitatum lists the governor (') of Britannia II as being equestrian rank, making it unlikely to have been based in Londinium. The list of bishops who attended the 314 Council of Arles is patently corrupt