This article accompanies the fable
Keats and La Belle Dame sans Merci
Although the title, La Belle Dame sans Merci, comes from an early 15th century French poem, Keats' poem perhaps reflects the first appearance of the 19th century femme fatale. She is more dangerous than Helen of Troy in Faust or Venus in the Tannhäuser legend.
She was also a wonderful inspiration for the pre-Raphaelites. Here are two paintings on the subject, the first by Frank Dicksee around 1902, and the second by John William Waterhouse around 1893.