In ’ Tongues in Trees,’ a work on plantlore published by George Allen in 1891, I read at p. 48 :— “The pasque-flower, Anemone pulsalilla, a native in the fields near Royston, is there supposed to have grown from the blood of Danes slain in battle.
Pasque flowers (with luck) still grow on Therfield Heath just outside Royston. And of course the long barrow must be where the Danes are buried? Quote in Notes and Queries January 7th 1911.