John Keats (1795-1821) was one of the great English Romantic poets. 'La Belle Dame Sans Merci' is a haunting ballad describing a young knight whose very lifeblood and vitality have been drained by a beautiful but parasitic, fairylike vampire. This knight has now been left as an undead shell of his former self, alone on a barren hillside.
Haunting and Evocative
There are so many analyses of this poem; I have none to add. But, for me, it has always been haunting and faintly eerie--after all, " . . . her eyes were wild . . . "