The poem is written in unrhymed dactylic hexameter. This is an unusual meter in English poetry, although it was commonly used in ancient Greek and Latin poetry. The epics of Homer and Virgil are written in dactylic hexameter, and Longfellow thought it was the only suitable meter in which to write his own epic poem.

A dactyl is a poetic foot consisting of a stressed syllable followed by two unstressed syllables. A hexameter is a line of poetry containing six poetic feet. Poems written in dactylic hexameter are often in practice a mix of dactyls and spondees or trochees. A spondee is a poetic foot consisting of two stressed syllables; a trochee comprises a stressed syllable followed by an unstressed syllable. The spondee or trochee is often placed at the end of the line.

The following dactylic lines from the prelude end in a trochee, which is overwhelmingly Longfellow’s preferred method of concluding the lines in this poem: “This is the forest primeval. The murmuring pines and the hemlocks” (Line 1); “Leaped like the roe, when he hears in the woodland the voice of the huntsman?” (Line 8); and “Darkened by shadows of earth, but reflecting an image of heaven?” (Line 11).