The idea is simple: If there’s a fire in a tall building that blocks the main stairwell, people need an alternative way to evacuate, preferably one that is somewhat protected or at least far away from where the fire is happening. If you’re in a one or two story building, it’s pretty simple: just get out of any window or door. You may get hurt a little, but you’ll still be away from the fire. In the denser cities of the early United States, though, as the buildings grew taller, the options for evacuation became more complicated. High-profile, horrific building fires were a nearly constant plague in factories, tenements, office buildings, and theaters. The external fire escape seemed obvious to many: Bolt a metal staircase to the outside of the building with a landing below a window on each floor.