Henry David Thoreau, who wrote his famous “Civil Disobedience” essay after spending a night in jail for refusing to pay a poll tax, was an outspoken abolitionist and served as a conductor on the Underground Railroad in his hometown of Concord, Massachusetts. For two years, he lived simply and deliberately in a small, hand-built cabin near Walden Pond. The transcendentalist philosopher Ralph Waldo Emerson, a close friend, owned the land. Thoreau died at 44 of a flare-up of tuberculosis, which he had contracted as a student at Harvard University.