Being real and not fictitious would seem to suggest the God damn Mongolians (always breaking down my wall). Having never existed though ,King Arthur and his Knights would be immortal and impossible to kill ? Tricky one.

I used to take my son and his mate to Tintagel, not far from where I live, to play knights with their wooden swords, but although there are the remains of a castle there is no trace of King Arthur or his Knights. The legend though helped sustain the British through the dark ages and may have helped instil that gung ho, fuck everyone invading us again and again, lets take over the world spirit that led to an Empire.