The shades of night were falling fast,
As through an Alpine village passed
A youth, who bore, 'mid snow and ice,
A banner with the strange device,
This is the first stanza of Longfellow's poem "Excelsior". There are eight more stanzas of exactly the same meter and rhyme scheme. Longfellow wrote this poem in extremely regular iambic tetrameter. There are four iambic (unstressed syllable followed by a stressed syllable) feet in each of the first four lines of each stanza, and each stanza is ended by the fifth line containing the world "Excelsior!". The rhyme scheme is aabb -refrain - ccdd -refrain - eeff -refrain, etc. The refrain is the repeated fifth line of each stanza ("Excelsior").
This poem is not only written in tetrameter, each of the tetrameter lines contain exactly eight syllables (four stressed and four unstressed). The lines can all be read iambically, with only a few forced or unnatural stresses (such as line 6 "Flashed like, as opposed to the more natural "Flashed like", or the similar line 30 "Utterred" as opposed to "Utterred"). Longfellow was a master of this form, and it is difficult to find other stretches of poetry 45 lines long with this high rate of regularity.
While this poem is not written in ballad meter (quatrains composed of alternating iambic tetrameter and trimeter) its subject matter is one of a ballad. Ballads were usually songs with the subject of love, courage, adventure, or tragedy. This poem treats its subject much like a ballad would be constructed, with the repetition of the speakers (the old man, the maid) and the repeated warnings against disaster. But the form is regular iambic tetrameter punctuated by a repeated refrain of iambic dimeter ("Excelsior"!).