According to legend, the Great Chicago Fire, which burned from October 8 to 9, 1871, was started by a cow (usually described as belonging to a Mrs. O’Leary) kicking over a kerosene lantern on De Koven Street. But the exact cause is unknown, and many theories exist about how it started—from one of the O’Leary’s cows, who all perished in the blaze, to speculation that a meteor broke apart, raining fiery particles in the region.

The Chicago Historical Society cataloged the damage: “The so-called ‘Burnt District’ encompassed an area four miles long and an average of three-quarters of a mile wide—more than two thousand acres—including more than 28 miles of streets, 120 miles of sidewalks, and more than 2,000 lampposts, along with countless trees, shrubs, and flowering plants in ‘the Garden City of the West.’ Gone were 18,000 buildings and some $200 million dollars in property, about a third of the valuation of the entire city. Around half of this was insured, but the failure of numerous companies cut the actual payments in half again. One hundred thousand Chicagoans lost their homes, an uncounted number their places of work.”

Chicago resident Julia Newberry described the aftermath in her diary in an entry dated October 17 (published in 1933 by W. W. Norton): “The fire began at twelveth (sic) street on Sunday night Oct. It swept the two magnificent avenues, & every building on the South side from twelveth street to the river. The Court House, with the original copy of Father’s will & no one knows how many invaluable papers, legal documents, records, the beautiful Crosbie Opera house, a perfect bijou (sic) of a theatre, all the banks, insurance offices, railway depots, churches, & block after block of stores, unequalled any where. And then oh misery, the fire, the red, angry, unrelenting fire, leapt across the [Chicago] river, & burnt & burnt, till Mr. Mahlon Ogden’s house was the only one left standing up to Lincoln Park. Yes the whole North Side is in ashes ….”

Though the United States has suffered other disastrous fires, including an 1835 blaze in New York City, which destroyed some 500 buildings, the Chicago Fire is the worst fire tragedy in the recorded history of North America. The damage was not limited to the city of Chicago: Sparks lit forest fires that destroyed more than a million acres of Michigan and Wisconsin timberland, burning from October 8 to October 14. These fires were responsible for the loss of more than 1,000 lives in the logging town of Peshtigo, Wisconsin, and in 16 surrounding communities.

Like the Great Fire of London 200 years earlier, a flurry of construction activity followed in the city, making Chicago one of the United States’ most architecturally impressive urban centers. In fact, the fire was the impetus for the development of the Chicago School of Architecture, also called the commercial style (since most of it was devoted to office buildings, warehouses, and department stores). The Chicago School was instrumental in establishing the modern movement of architecture in the United States.