Airplane windows are good for more than just snapping photos from 30,000 feet.

As  this video from Real Engineering explains, round airplane windows are actually a major safety innovation that keeps planes from disintegrating mid-flight.

The history of the round airplane window descended from -- as most great aviation innovations do -- fuel efficiency. As commercial travel became more popular, airplanes started flying at higher altitudes to avoid turbulence and drag.

However, higher altitudes came with problems, like the fact human beings can't really survive at 30,000 feet. Pressurized cabins were invented to allow passengers to, uh, live and the fuselage became cylindrical to withstand the internal pressure. As a plane increases altitude, there is less pressure on the outside of the plane, but the internal cabin pressure changes only subtly. These two differing pressure systems create a pressure difference, which causes the plane to (slightly) expand.

When planes had square windows, this expansion meant catastrophe. The pressure would build on the corners of the windows until the body of the plane cracked. This happened to three planes in 1953, causing tragic crashes that killed 43 passengers.

Today, all airplanes have rounded windows and go through rigorous FAA testing.