Rosemary's mention of the line in the Keats poem
“The sedge has withered from the lake, and no birds sing”
prompted me to find the poem and read it.

That poem, La Belle Dame Sans Merci
(The Beautiful Lady Without Mercy)
was dashed off quickly by Keats in 1819 and subsequently dismissed by him.
In it, a knight becomes enslaved by the love of an enchantress, then learns that he is one of many so enslaved. It became one of his most celebrated poems. 

Inspired 74 years later by Keats' poem (1893,) John William Waterhouse painted
his famous La Belle Dame Sans Merci, seen above,
a knight with a young beauty at twilight.

Notice the word “gloam” in the second-to-the-last stanza.
Gloam means twilght.

La Belle Dame Sans Merci

Oh what can ail thee, knight-at-arms,
    Alone and palely loitering?
The sedge has withered from the lake,
    And no birds sing.

Oh what can ail thee, knight-at-arms,
    So haggard and so woe-begone?
The squirrel's granary is full,
    And the harvest's done.

I see a lily on thy brow,
    With anguish moist and fever-dew,
And on thy cheeks a fading rose
    Fast withereth too.

“I met a lady in the meads,
    Full beautiful – a faery's child,
Her hair was long, her foot was light,
    And her eyes were wild.”

“I made a garland for her head,
    And bracelets too, and fragrant zone;
She looked at me as she did love,
    And made sweet moan.”

“I set her on my pacing steed,
    And nothing else saw all day long,
For sidelong would she bend, and sing
    A faery's song.”

“She found me roots of relish sweet,
    And honey wild, and manna-dew,
And sure in language strange she said –
    'I love thee true'.”

“She took me to her elfin grot,
    And there she wept and sighed full sore,
And there I shut her wild wild eyes
    With kisses four.”

“And there she lulled me asleep
    And there I dreamed – Ah! woe betide! –
The latest dream I ever dreamt
    On the cold hill side.”

“I saw pale kings and princes too,
    Pale warriors, death-pale were they all;
They cried – 'La Belle Dame sans Merci
    Hath thee in thrall!'”

“I saw their starved lips in the gloam,
    With horrid warning gaped wide,
And I awoke and found me here,
    On the cold hill's side.”

“And this is why I sojourn here
    Alone and palely loitering,
Though the sedge is withered from the lake,
    And no birds sing.”