The available evidence includes the scant contemporary and near-contemporary written record, and archaeological and genetic information.[a] The few literary sources tell of hostility between incomers and natives. They describe violence, destruction, massacre, and the flight of the Romano-British population. Moreover, there is little clear evidence for the influence of British Celtic or British Latin on Old English. These factors have suggested a very large-scale invasion by various Germanic peoples. In this view, held by the majority of historians until the mid- to late 20th century, much of what is now England was cleared of its prior inhabitants. If this traditional viewpoint were to be correct, the genes of the later English people would have been overwhelmingly inherited from Germanic migrants.
However, another view, probably the most widely held today, is that the migrants were fewer, possibly centred on a warrior elite. This hypothesis suggests that the incomers, having achieved a position of political and social dominance, initiated a process of acculturation by the natives to their language and material culture, and intermarried with them to a significant degree. Archaeologists have found that settlement patterns and land use show no clear break with the Romano-British past, though there were marked changes in material culture. This view predicts that the ancestry of the people of Anglo-Saxon and modern England would be largely derived from the native Romano-British. The uncertain results of genetic studies have tended to support both a predominant amount of native British Celtic ancestry and a significant continental contribution resulting from Germanic immigration.
Even so, if these incomers established themselves as a social elite, this could have allowed them enhanced reproductive success (the so-called 'apartheid theory'). In this case, the prevalent genes of later Anglo-Saxon England could have been largely derived from moderate numbers of Germanic migrants. This theory, originating in a population genetics study, has proven controversial, and has been critically received by a number of scholars.
By 400, the Roman provinces in Britain (all the territory to the south of Hadrian's Wall) were a peripheral part of the Roman Empire, occasionally lost to rebellion or invasion, but until then always eventually recovered. That cycle of loss and recapture collapsed over the next decade. Eventually, around 410, although Roman power remained a force to be reckoned with for a further three generations across much of Gaul, Britain slipped beyond direct imperial control into a phase which has generally been termed "sub-Roman".
The history of this period has traditionally been a narrative of decline and fall. However, evidence from Verulamium suggests that urban-type rebuilding, featuring piped water, was continuing late on in the fifth century, if not beyond. At Silchester, signs of sub-Roman occupation are found down to around 500, and at Wroxeter, new baths have been identified as of Roman-type.
The writing of Patrick and Gildas (see below) demonstrates the survival in Britain of Latin literacy and Roman education, learning and law within elite society and Christianity, throughout the bulk of the fifth and sixth centuries. Also, signs in Gildas' works indicate that the economy was thriving without Roman taxation, as he complains of luxuria and self-indulgence. In the mid fifth century, Anglo-Saxons begin to appear in an apparently still functionally Romanised Britain.