On the morning of the 7th of November, 1940, travellers on the Tacoma Narrows Bridge in the state of Washington noticed something strange. The roadway suspended between the bridge’s concrete pillars was oscillating and twisting – gently at first, and then more and more dramatically. Soon enough almost the entire central span of the bridge was in motion, rippling wildly. At around 11am, whatever force was causing this movement proved too powerful, and the bridge collapsed into the water below. What exactly had happened was, at that stage, a mystery to almost everyone.