Have you ever noticed that at the beginning of most scary movies everything seems pretty normal? Usually, everybody is having just a grand old time, there's some light humor, birds are chirping—yadda, yadda, yadda. If you read the first lines of "Eldorado," you'll get that same sense: "Gaily bedight,/ A gallant knight" (1-2). Here we have a happy little rhymed couplet that seems to suggest a poem to come of sunshine and lollipops.
But slow your roll there, Shmoopers. It's not all high fives and good times in this knight's world, as the sounds of the poem soon indicated. We talk a lot about the meter and rhyme of the poem in "Form and Meter," so go check out that section for the scoop. Here, we want to look at how the poem's use of other sounds help to support its eventually dark and creepy turn.
For example, for such a short poem, "Eldorado" has a ton of alliteration. That's when multiple words begin with the same sound. In stanza 1, we have "sunshine," "singing," "song," and "search." And since this is the initial, happy set-up of the poem, we think that all these S sounds give us a peaceful sound, like a gentle breeze or babbling brook in our ears.
But then, things take a turn to sadville. The alliteration of stanza 2 comes with the F sound: "fell" and "found." Avoiding the crass and easy joke about F words, we can tell you that the sound here is more forced, less easy-on-the-ears than stanza 1's S alliteration. Appropriately, this comes as the knight starts to realize that he's not going to find Eldorado after all.
In stanza 3, we don't get alliteration so much as consonance. Once again we have S sounds, but now they are more jumbled together ("as his strength"), than nicely, neatly organized in the front of words as in stanza 1. Things are going from bad to worse for our knight, and these sounds reinforce that.
The same can be said for the poem's final stanza, where the sheer amount of alliteration ("mountains" and "Moon," "Shadow" and "shade," and the repetition of "ride") seems to mock the poor knight. He realizes that he'll never find Eldorado, but the sounds here mimic the beginning unity of the first stanza. Those happy little alliterations of stanza 1 are long gone, and now we have a kind of over-the-top alliteration that seems to rub his disappointment in the knight's face. Or in his ear. Of course, his ear is on his face, so maybe both are right!