Rows of polished weapons rising "from floor to ceiling" look to Longfellow like the pipes of a church organ, and from that one comparison he builds an entire argument against war. The opening line is almost a tour guide's patter: "This is the Arsenal." Then the conceit takes over. The "burnished arms" are "silent pipes," but the silence is deceptive, because every organ waits for a player. In the second stanza the player arrives: "the death-angel touches those swift keys," and the music that follows is a "dismal Miserere," a Latin prayer for mercy turned into a dirge.
The middle of the poem is a catalogue of noise. Longfellow repeats "I hear" and sweeps across centuries and continents: the "Saxon hammer" ringing on helmets, the Norseman's song in a "Cimbric forest," the "Tartar gong," a Florentine battle-bell, Aztec priests beating drums "made of serpent's skin." War here is not one nation's misfortune but a single sound that has echoed "through the ages" until it reaches "our own." The detail then sharpens. Stanza six piles up fragments without a main verb ("The tumult…; The shout…; The soldiers' revels…; The wail of famine…"), so the grammar itself seems to crowd and jostle. The climax is "the diapason of the cannonade." Diapason is another organ term, meaning the full, rolling range of the instrument, so even at its loudest the metaphor holds.
The form is steady while the content is chaotic. The poem runs to twelve quatrains of rhymed iambic pentameter, with the rhymes alternating. This regularity gives the poem a hymn-like stateliness that suits its instrument. Several rhymes carry extra weight. Feminine rhymes such as "ceiling/pealing" and "dreary/Miserere" leave a lingering, bell-like echo. The pairing of "terror" with "error" quietly makes Longfellow's point that fear and ignorance are linked. The rhyme "cease/Peace" arrives just when the noise dies away.
In stanza eight the poem stops listening and starts accusing. "Is it, O man, with such discordant noises… / Thou drownest Nature's sweet and kindly voices?" The charge is that war is not only cruel but out of tune with nature and heaven. The next stanza turns practical. If "half the power" and "half the wealth, bestowed on camps and courts," went instead to "redeem the human mind from error," then "there were no need of arsenals or forts." Naming "courts" alongside "camps" puts rulers in the dock with soldiers. The remedy is education rather than disarmament by force. The warning that a nation raising its hand "against a brother" will wear "the curse of Cain" gives the argument a biblical sternness.
Then the sound drains away: "The echoing sounds grow fainter and then cease." A bell replaces the cannon, and the voice of Christ says "Peace!" The final stanza opens with that very word, stressed on its first syllable. After so much smooth iambic movement, this small inversion lands like a struck note. The organ returns too, but transformed. "War's great organ" no longer "shakes the skies," and its "brazen portals" (the brass pipes and gates) give way to "the holy melodies of love." The poem does not abolish its central image; it redeems it.
What makes the poem worth reading is this discipline. Longfellow, one of the best-known American poets of the nineteenth century, does not simply announce that war is bad. He makes the reader hear it, then hear the alternative, using one sustained image from start to finish. His faith that humanity will outgrow its arsenals may strike a modern reader as hopeful to the point of innocence. Yet the question at the poem's centre, whether people will keep drowning "Nature's sweet and kindly voices" with their own machinery, has not gone out of date.