The one thing that seems to have flourished during the period (following the withdrawal of the Romans in 410 A.D.)
is the Church.
The Christian Church of the Celts had never relied upon Rome,
both on account of its distance and also because of its probable Eastern origin.
It was therefore the sole organisation in the country,
particularly in the western parts of the island, which did not seem to be weakened by the Roman withdrawal.
Indeed, it may be true to say that it became stronger on that account
since it tended to become associated with a feeling of nationalism,
especially when its followers became pitted against the pagan Anglo-Saxons.
It was at this period that Wales became a land of saints with Erging, or Archenfield,
that land which lay between the Wye and the Monnow with Monmouth at its tip,
more especially so.
It was from Archenfield that St. Dyfrig (Dubricius) came to teach the Faith at Hentland near Ross.
It was from Archenfield too that St Briavel came to found his cell at St. Briavel's Stowe in the glen above the Wye.
The text above is from:
by R.J. Mansfield
publisher: the author 1964