Härke and Michael Wood estimate that the British population in the area that eventually became Anglo-Saxon England was around one million by the start of the fifth century; however, what happened to the Britons has been debated. The traditional explanation for their archaeological and linguistic invisibility is that the Anglo-Saxons either killed them or drove them to the mountainous fringes of Britain, a view broadly supported by the few available sources from the period. However, there is evidence of continuity in the systems of landscape and local governance, decreasing the likelihood of such a cataclysmic event, at least in parts of England. Thus, scholars have suggested other, less violent explanations by which the culture of the Anglo-Saxons, whose core area of large-scale settlement was likely restricted to what is now southeastern England, East Anglia and Lincolnshire, could have come to be ubiquitous across lowland Britain. Härke has posited a scenario in which the Anglo-Saxons, in expanding westward, outbred the Britons, eventually reaching a point where their descendants made up a larger share of the population of what was to become England. It has also been proposed that the Britons were disproportionately affected by plagues arriving through Roman trade links, which, combined with a large emigration to Armorica, could have substantially decreased their numbers.