Henry David Thoreau was born on July 12, 1817, in Concord, Massachusetts. He began writing nature poetry in the 1840s, with poet Ralph Waldo Emerson as a mentor and friend. In 1845 he began his famous two-year stay on Walden Pond, which he wrote about in his master work, Walden. He also became known for his beliefs in Transcendentalism and civil disobedience, and was a dedicated abolitionist.