Who was King Arthur? Where did he live? Was he even real? All valid questions, and hotly disputed ones at that. While the English and Welsh have continually claimed Arthur as their own, the only historical Arthur of the time was Scottish. If this is indeed the personage that the tales all point back to, then us Scots ought to feel hard done by (we do anyhow), because so many English Kings have used the story of Arthur, King of the Britons in an English context, as fabricated by Geoffrey of Monmouth, as giving them precendent to rule over the Scots as overlords.
The real Athur was most likely the son of King Aidan of the Scots, who had crossed into Scotland from Northern Ireland and established a kingdom in Argyll. The Scots would later supplant the native Picts, and on their arrival in Scotland would have had the Picts and Britons as their near neighbours. All of these factions were to unite to fight against a common enemy, the Saxons, who were constantly pressing Northwards, particularly against the Britons, who found themselves in a dangerous buffer zone across central and lowland Scotland. Arthur was a prominent figure in the ensuing battle, possibly leading the federation of Kings into battle, and while there is little historical record of the man, perhaps the vigour and bravery he displayed before his death in that battle, earned him a reputation which lasted for centuries.
So, we can see how history has again been perverted for propaganda. King Arthur actually fought against the English, not for them. The Britons were later driven out of their Scottish kingdom and formed a new kingdom in Wales, which is why legends of King Arthur persisted there. The Romans had built a fort at Camelon or Camelot, near the Antonine Wall, close to Falkirk, and it was most likely from there that Arthur led his men out against the Saxons. To think of the number of visitors to Tintagel Castle, who have no idea who Arthur really was. If anyone wants to read a truly detailed and wonderful explanation of Arthur's Scottish origins, then there is a free book: Arthurius - Quest For Camelot by David F. Carroll, available for download online. It's an excellent read and clarifies the matter far more concisely than I could in these few paragraphs!