On October 8, 1871, flames sparked in the Chicago barn of
Patrick and Catherine O’Leary, igniting a two-day blaze that
killed between 200 and 300 people, destroys 17,450 buildings,
left 100,000 homeless and caused an estimated $200 million
(in 1871 dollars; more than $4 billion today) in damages.

Legend has it that a cow kicked over a lantern in the O’Leary
barn and started the fire, but other theories hold that humans
or even a comet may have been responsible for the event that
left four square miles of the Windy City, including its business
district, in ruins.