Byron is said to have written these lines after seeing a cousin of his in mourning, in a black dress covered with spangles. Hence the opening image: a beauty that «walks like the night of cloudless climes and starry skies», made of the best of dark and bright at once.
The poem belongs to the Hebrew Melodies (1815) and is an un-Byronic kind of praise: no scandal, no irony, only calm. The beauty he describes is not merely physical — a smile, a blush, a tress — but the outward sign of a mind at peace and an innocent heart. Three sestets of an almost musical serenity.