Byron composed “She Walks in Beauty” in iambic tetrameter, which is a meter that consists of four iambic feet per line. (Recall that an iamb is a metrical foot that follows an unstressed–stressed pattern, as in the words “im-paired” and “se-rene.”) The choice to use iambic tetrameter likely stemmed from the fact that Byron thought of the poem as a song. Indeed, this text was first published in a collection titled Hebrew Melodies, the poems in which were meant to be set to traditional Jewish tunes. When Byron wrote the poem at the end of the seventeenth century, poets generally preferred iambic pentameter, since the slightly longer five-foot line approximates the rhythms of everyday speech. By contrast, the shorter lines of iambic tetrameter have more of a sing-song rhythm appropriate for ballads and other verse forms that are frequently used for song lyrics. It’s probable, then, that Byron chose iambic tetrameter to amplify the poem’s musicality.

Byron’s musical intentions for the poem likely also explain the strict regularity of the meter throughout. There are very few variations in the iambic rhythm. Consider the opening stanza as an example (lines 1–6):

     She walks | in beau- | ty, like | the night
     Of cloud- | less climes | and star- | ry skies;
     And all | that’s best | of dark | and bright
     Meet in | her as- | pect and | her eyes;
     Thus mel- | lowed to | that ten- | der light
     Which hea- | ven to gau- | dy day | de-nies.

This passage contains only two minor deviations from the otherwise strict iambic rhythm. The fourth line begins with a trochee, which is a metrical foot that simply reverses the iambic stress pattern by starting with a stressed syllable and ending with an unstressed syllable. This trochee appears exactly halfway through the stanza, marking the sestet’s midpoint with a moment of syncopated rhythm. The meter then returns to perfect iambic regularity until the final line, the second foot of which is an anapest. An anapest is a three-syllable foot that consists of two unstressed syllables followed by a stressed syllable. Byron’s use of an anapest in the final line introduces another rhythmic ornament that again varies the meter, this time preparing the reader—or, better, the listener—for the end of the verse. Such a strategy is typical in song lyrics, which often subtly vary the rhythm at key moments that help guide the listener’s ear.