Thoreau, HENRY DAVID (1817-62), an eminent American prose-writer and naturalist, was born in Boston, United States, and became a graduate of Harvard University at the age of twenty. For three years he acted as a schoolmaster, but his strong opposition tot he slave trade and constant efforts in favour of abolition brought him into conflict with the advocates of slavery, and he was obliged to give up his calling. He had from an early age been deeply interested in animal and vegetable life, and withdrew into a solitude in Walden Wood, where he had built a small retreat, and pursued his natural history studies. The result is seen in his exquisite book, Walden: or, Life in the Woods (1854), which became immensely popular. He settled in Concord finally, where he followed the trade of a pencil-maker. He wrote largely for the periodicals, and published A Week on the Concord and Merrimack Rivers and other works.