Nibelungenlied

A few bits survived: Beowulf in England, the Nibelungenlied in Germany, and some stray fragments here and there.

No one knows exactly how the belief in cruentation got its start, but one of the earliest mentions on record is in the sixth century, in the epic Germanic poem Nibelungenlied.

Not exactly in Wagner’s stage instructions but a generous nod to the actual Nibelungenlied where Hagen transmutes to hero.

The romances of the Heldenbuch are of varying poetic value; only occasionally do they rise to the height of the two chief epics, the Nibelungenlied and Gudrun.

This is in fact truer of the "Nibelungenlied" than of almost any other great poem of the kind, whatever its time and place of origin.