According to archaeological evidence, Caer Ceri continued as a centre for
civic life in the 440s; the defences were repaired, flood prevention work was carried out
on one of the gates, and the piazza of the forum was kept clean. But in 443 the whole
Roman world was swept by a plague, the severity of which has been compared to the Black
Death, and this hit Britain in around 446. At the same time as the Anglo-Saxon mercenaries in
the east revolted, unburied bodies were to be found in Caer Ceri's streets, and the town
seems to have contracted to some small wooden huts inside the amphitheatre.
The Romano-British must have recovered from the mid-century plague. The next major event for the territory was Ælle's attack on
Mons Badonicus in circa 496. The
route the Saxon forces took was probably westwards along the upper
Valley and through the Goring Gap.
It seems creditable to assume that the north-facing Wansdyke, constructed in the fifth or
sixth centuries (and which roughly follows in part the proposed upper section of Caer Baddan's
eastern border where it leads to the northwestern border of Caer Celemion), was put up by
sub-Roman forces in Wiltshire in the face of just such a threat.
It could either have been constructed to ward off this very
attack from the direction of the Thames Valley (and perhaps channel the attackers towards Badon), or in response to
it, to ensure that no future attacks of this nature could take place. In
that it was very effective, until the
West Seaxe conquered the
heart of Wiltshire in 552.
No doubt greatly heartened
by their victory at the end of the century, the sub-Roman presence continued to hold out.
For much of the early sixth century (at least until 534, and maybe as late
as 560) they remained in general unmolested.
In 577, the West Saxons set great store by the fact that the final kings of the three
cities were killed fighting them at the Battle of Dyrham (Gloucestershire).
The territory was taken over by the Hwicce,
who apparently merged with the existing Briton population. The West Wansdyke region of Caer Baddan
seems to have remained in Dumnonian hands (or those of Glastenning) until
597-611, when it fell to the West Seaxe.