thumb|right|300px|[[Roman Britain around AD 410, without speculative provincial borders.]]
Flavia Caesariensis (Latin for "The Caesarian province of Flavius"), sometimes known as Britannia Flavia, 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. It seems to have been named after Chlorus's family and was probably located beside Maxima Caesariensis, but their positions and capitals remain uncertain. At present, most scholars place Flavia Caesariensis in the southern Pennines, possibly reaching the Irish Sea and including the lands of the Iceni. Its capital is sometimes placed at Lindum Colonia (Lincoln).
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left|200px|thumb|The traditional arrangement of the late Roman provinces after [[William Camden|Camden, placing Flavia in central England. On the basis of modern archaeology, it's known that at least Corinium was part of Britannia I.]]
left|200px|thumb|Another possible arrangement of the late Roman provinces, with more northerly borders for Flavia
History
Following the Roman conquest, Britain 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). 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 Flavia being of 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