The summer and early fall of 1871 had been unusually dry in the Midwest. On the night of October 7, firefighters in Chicago battled a large fire on the city’s west side. The city had a small fire fighting crew and lost a few water cannons in the battle, too, so both they and their equipment were worn out when, the next night, Sunday October 8, another fire came to life on the West Side.

The Sunday night fire spread quickly. Almost the entire city was built from lumber – not just houses and buildings, but sidewalks that allowed residents to walk above the muck of the city built on a swamp, and the major roads, which were planked. The city’s wealth was built on lumber imported from the Northwest, which was planed and sawed by dozens of lumberyards in the city. Areas with lumberyards were quick to spark, with the stacks not only of lumber, but also of mounds of highly flammable sawdust.

In addition to the dry weather, the night of October 8 was particularly windy. The wind was blowing to the northeast, so the fire promptly jumped the south branch of the Chicago River and headed toward the heart of the city. The firefighters, exhausted from the night before, quickly lost control of the flames.

These conditions were the makings of a disaster. By 1:30 am the fire had spread more than a mile from where it had started and had engulfed most of the buildings in the downtown areas. City hall and the courthouse burned. By 3:30am the city’s main pumping station had burned to the ground and all hope of quelling the flames was extinguished.

The fire jumped the north branch of the river early on Monday and wrought havoc on the north side of the city. It continued to burn until early on Tuesday October 10, when a light rain smothered the major flames.

But by then, a third of the city’s population – about 100,000 people – had lost their homes and about 300 people had lost their lives. Later insurance leaders estimated that nearly $200 million dollars of property had been destroyed. That’s about $2 to $4 billion in today’s dollars.

Later there would be a number of explanations for how this fire started. Some claimed to have seen meteors that night and theorized that one had hit a wooden structure on the west side of town and set it ablaze. A modern-day scholar argues that a man dropped a burning cigarette in a barn and the flames quickly spread. But one theory has stuck: a clumsy Irish woman had allowed her cow to kick over a burning lantern in the process of the Sunday evening milking.

It’s unlikely that Mrs. O’Leary and her cow were the true culprits behind the Chicago Fire of 1871: if nothing else, anyone who has once milked a cow, let alone spent her entire life doing so, would be unlikely to place a lantern within kicking distance of the animal. But the O’Leary theory provided a colorful story to explain the fire that decimated the city. Plus, it allowed the city to blame an already despised class of poor working Irish immigrants.

While no one can deny the horror and devastation the Chicago Fire created, the hindsight of history has allowed us the vision of a thin silver lining.

City leaders set their minds to rebuild the city, bigger and better than ever. They accomplished that task in less than a year, and kept on going. They prohibited wood construction within city limits. Since brick was an expensive building material, this forced many poorer families to move beyond city limits. This development both helped expand the city’s boundaries and guaranteed that the center of the city was relatively fire proof in the coming years. Another change the fire created was that officials built straighter streets. In the downtown area, sidewalks, which had varied wildly in height before the fire, were standardized. The call for workers from the East Coast and abroad flooded the labor market in the following year, causing conflict between labor unions and owners of industry, but also eventually provided a workforce for the bourgeoning industrialization of the city.

The results of the fire were a mixed bag, to be sure, but the Great Chicago Fire ultimately provided the tabula rasa that business leaders needed to remake the city and push it into place as the center of trade for the continent.

Even today, Chicagoans commemorate October 8 as the destruction and rebirth of their city: the birth of modern Chicago, the birth of the Second City.