“Tithonus” begins with a bird’s-eye view of a withering world. The poem’s speaker looks out from a great height over vast stretches of space and time. As he watches, “the woods decay and fall”; clouds gather and rain descends; generations of people are born, farm the land, and die; and the long-lived “swan” at last dies, too.
These melancholy visions are seen through the eyes of Tithonus, the legendary figure after whom the poem is titled. In Greek mythology, Tithonus was a Trojan prince who fell in love with Eos, the goddess of the dawn. Wanting to prolong their joy infinitely, Tithonus begged his divine lover to immortalize him. She did so—but forgot to specify that he should be immortally young. Tithonus thus became unimaginably old: eternally wasting away, unable to die.
Tithonus’s first words suggest that he’s already deep into his terrible, endless old age. The weary epizeuxis of “the woods decay, the woods decay and fall” suggests that he’s seen forest after forest rise and rot away, frail as flowers, while epochs pass. And the polysyndeton of "man comes and tills the fields and lies beneath" captures the one-thing-after-another circle of life ticking ceaselessly away beneath Tithonus’s gaze.
His other images suggest that his broad, immortal view of the world has only saddened him. Looking on the heavy “vapours” that gather before rainfall, he personifies them, imagining that when the rain comes, they mournfully “weep.” And his allusion to the swan, which lives “many a summer” before it dies, raises echoes of a poignant old legend: swans were said to be astonishingly long-lived, and to be silent until the moment of their deaths, when they sang lovely, unearthly songs.
These are visions of release as much as sorrow and death. The “vapours weep their burthen to the ground”; in other words, as they cry, a burden falls from them, and they’re freed. Readers might imagine those soft clouds melting away not long after their tearful showers. And the swan’s death hints at a climactic, transcendent beauty, a moment of glory that comes just before it's all over—and because it’s all over.
Such releases are not for the immortal Tithonus. In this dramatic monologue (a poem spoken in the voice of a particular character), Tithonus will lament that, while he knows the circle of life and death more intimately than any other human being ever could, he can’t participate in it himself. As he puts it, “Me only cruel immortality / Consumes.” Death devours everyone else; for him, it’s eternal life that, like Prometheus’s vulture, gnaws away at him endlessly without ever releasing him into oblivion. The divine gift of immortality has become, for Tithonus, an ironic and nightmarish curse.
Tennyson tells this haunting tale in blank verse—that is, unrhymed iambic pentameter. That means that each of the poem’s lines uses five iambs, metrical feet with a da-DUM rhythm (with occasional variations for flavor). Here’s how that sounds in line 1:
The woods | decay, | the woods | decay | and fall,
This is the grand rhythm of Shakespearean tragedy and Miltonic epic, and it lends Tithonus’s story a sorrowful weight.