"O what can ail thee, knight-at-arms,/ Alone and palely loitering?"
The opening lines introduce the first two of the poem's three significant characters: a weary knight wandering alone on the hillside. We learn two significant pieces of information that will be crucial to interpreting the poem: the knight is exhausted and in poor health and, traveling without a companion, he is vulnerable to the supernatural forces lurking in the woods.
"The sedge had wither'd from the lake/ And no birds sing."
These lines continue to establish the poem's setting and foreboding atmosphere. The withered grasses reveal that the poem takes place during late autumn or winter, creating the image of a dark, cold, and grey landscape. The birds' silence indicates an absence of life, and suggests that something sinister approaches. The monosyllabic line 'And no birds sing' stresses the end of the stanza, also adding to the sense of danger. This refrain is repeated in the final stanza, as is typical of the ballad form.
"La Belle Dame sans Merci Thee hath in thrall!"
In his dream, the knight sees pale kings, princes, and warriors who also succumbed to the woman's spell. They tell him that now he, too, is entranced, and their fate doesn't bode well for his chances of escaping.
