BY THE SPRING of 1844 Henry David Thoreau had accomplished almost nothing. He was 26 years old and had spent the better part of his life more or less adrift. In the seven years after graduating from Harvard, Thoreau tried to support himself in a variety of ways, as a teacher, tutor, writer, surveyor, and as a general handyman. He lived for a time with his friend and mentor, Ralph Waldo Emerson, and later in New York City with Emerson's brother, only to return to Concord to reside once again with his own family.

Then, in the summer of 1845, Thoreau built a solitary cabin at Walden Pond, and set about the great venture in simplified living for which he would become famous. Over the course of the next two years - some of the most productive of Thoreau's life - he recorded meticulous observations of nature in his journal, revised the manuscript of his first major work, "A Week on the Concord and Merrimack Rivers," and completed the first draft of his magnum opus, "Walden, or Life in the Woods." It is in "Walden" that Thoreau announces "the mass of men lead lives of quiet desperation," and it is here that he famously urges his readers to "simplify, simplify." "Walden" established Thoreau's reputation as one of America's great literary figures, and to this day, both the book and the pond are synonymous with naturalism, environmentalism, and the austere pursuit of self-reliance.

So what finally motivated Thoreau to leave the comforts of his family home and embark on this radical experiment? The most common explanation is that Thoreau did so at the urgings of Ralph Waldo Emerson, William Ellery Channing, and other friends who were eager to see a promising young man fulfill his potential.

But there is one curious event in the life of Henry David Thoreau that has received little attention, and which may have been a formative event, influencing not only his decision to sequester himself at Walden Pond, but also the development of his environmentalist philosophy. On April 30, 1844, Thoreau started a blaze in the Concord Woods, scorching a 300-acre swath of earth between Fair Haven Bay and Concord. The fire was an accident, but the destruction of valuable woodland, the loss of firewood and lumber, and the narrowly avoided catastrophe that almost befell Concord itself angered the local residents and nearly ruined Thoreau's reputation. For years afterward, Thoreau could hardly walk the streets of his hometown without hearing the epithet "woods burner."