On October 8, 1871, a fire started in the barn behind the O’Leary cottage and ripped through nearly four square miles of Chicago. At the time, pretty much the entire city was made of wood, including the roads and sidewalks.
Due to poor firefighting equipment and inadequate fire codes, the blaze burned for two days, killing approximately 300 people, leaving 100,000 homeless and destroying about $200 million in property, a total of 17,450 buildings.
Legend has it that the fire was started after a cow kicked a lantern over in the barn, though there are plenty of other theories out there.
On the same day the Great Fire broke out, another fire began in Peshtigo, Wisconsin, where more than 1,000 people lost their lives.