Context and death and Percy Shelley
Half of the Great English Romantic poets died young and surrounded by tragedy. John Keats died of Tuberculosis at 26. Gordon “The Lord” Byron was 36 when he died from over leeching while fighting a cold. William Wordsworth, Samuel Taylor Coleridge, and William Blake all died at 71, 62, and 70 respectively.
Percy Shelley was 29 when he drowned after his boat sank off the coast of Italy. After Percy's body washed ashore his wife and friends cremated him on a beach near where he was found. His wife, Mary Shelley, the author of Frankenstein, kept Percy's heart.
29 years after her husband's death Mary Shelley died of brain cancer. When they went through her stuff they found Percy’s heart wrapped in pages of Adonais, a poem Percy had written for Keats after his death. As junkets notes in the Adonais node, the last lines of the poem are prophetic of Percy's own death, which occurred one year after he wrote the poem.
Mary Shelley was actually Percy’s second wife. His first wife, Harriet Westbrook, was pregnant when she drowned herself in London’s Hyde Park at the age of 20. She had married Percy four years before but he left her for Mary.
Percy and Mary Shelley had two children named Clara and William. They died at the ages of one and three. They died nine months apart from each other. Mary had had a miscarriage three years before. Mary Shelley’s mother, proto-feminist Mary Wollstonecraft, died due to complications after giving birth to Mary.
Only one of the Shelley's children, Percy Florence, survived until adulthood.
He lived into his 70s.
Sources
Abrams, M.H. ed. The Norton Anthology of Literature seventh edition, vol 2. 2000
Wasserman, Earl R. Shelley: A Critical Reading. Baltimore: Johns Hopkins, 1971
Swann, Karen Romanticism and the Insistence of the Aesthetic: Shelley's Pod People http://www.rc.umd.edu/praxis/aesthetic/swann/swann.html
World, The Wikipedia http://www.wikipedia.org