Gildas, about A.D.540, describes a Britain confined to the west of our island, which is very largely Celtic and not Roman.[1] Had the English invaded the island from the Atlantic, we might have seen a different spectacle.

The Celtic element would have perished utterly: the Roman would have survived.

As it was, the attack fell on the east and south of the island--that is, on the lowlands of Britain.
Safe in its western hills, the Celtic revival had full course.
[Footnote 1: How much of Britain was still British when Gildas wrote, he does not tell us.

But he mentions only the extreme west (Damnonii, Demetae); his general atmosphere is Celtic, and his rhetoric contains no references to a flourishing civilization.

We may conclude that the Romanized part of Britain had been lost by his time, or that, if some part was still held by the British, long war had destroyed its civilization.