Where Camelot may have been located.
No ruins, stone castles weren't the thing back then unless you reported directly to Rome. Real Rome (which was not doing much on the British front at the time, being busy with the whole I've Fallen And I can't Get Up thing) not nostalgic ideal Rome, which does not make good on imaginary purchase orders. Arthur would have used a wooden stockade. Surrounded by a really good stand of nettle (over my head tall when I was there, a scant 1500 years later July 22, 1981) it might be quite effective when the latest in armor is blue paint.