Now according to that A.D. 825 Welsh historian Nenni, it was at the Battle of Cat Coit Celidon against the Anglo-Saxons, that the Brythonic King Arthur led his Celtic Christian soldiers onward into war against the invaders. Significantly, the Christian King Arthur did so, precisely while shouldering a shield emblazoned with the Christian cross.
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Clearly, Arthur did so near the Scottish border. For the Celtic phrase "Cat Coit Celidon" means: "the Battle of Calendar Wood" (alias Caledonia).
Arthur was the Christian 'High-King' or Arh-an-Rhaig of the Britons. Several have attempted to locate him at Gelliwig alias Kelliwic in Cornwall, where he may indeed have had at least a summer palace in his large western domain (comprising the better part of Brythonic Britain all the way from Dumbarton in the north to Land's End in the south). The mediaevalist Sir Thomas Malory, who died in 1471, did so4 in his work on Arthur's death entitled Morte d'Arthur — which he is alleged to have compiled5 from much earlier sources.