Naturalist, writer, poet, and philosopher Henry David Thoreau was an American who lived from July 12, 1817, to May 6, 1862. His most well-known work, Walden, is a meditation on simple life in the natural world. He was a forerunner of ecological theory and environmental history, two major influences on contemporary environmentalism. In Concord, Massachusetts, Henry David Thoreau was born into a humble family. Between 1833 and 1837, he attended Harvard College for his studies. He worked as a land surveyor and continued to keep a two million-word notebook for 24 years, recording ever-more-detailed observations on the natural history of the town, which covered an area of 26 square miles (67 square kilometers). Thoreau never got married and never had kids. He proposed to Ellen Sewall, then 18 years old, when he was 23 years old, but she declined on the advice of her father. On May 6, 1862, Henry David Thoreau passed away. He was 44. After contracting TB in 1835, he intermittently experienced its effects. His final words, spoken while he was still conscious, were "Now comes good sailing," followed by the words "moose" and "Indian." In Concord, Massachusetts' Sleepy Hollow Cemetery, he was laid to rest.