Hoo boy, Parzival (by Von Eschenbach) is NOT just a tale about The Templars, King Arthur, Knights of the Round Table, and a boy raised in the forest by his mom
Starting on page 1, it’s drippin with esotericism and allegory, but also “hidden history” of some real events.
It is (as of the time of writing) still free on the Internet Archive here.
see also: The Band Rush and the song about the trees.

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See how “Parzival” influenced some characters from history you may not expect.