On a rainy August morning in 2018, a massive section of the Polcevera Bridge in Genoa, Italy, collapsed and killed 43 people. As emergency responders raced to rescue survivors, authorities began investigating the cause of the collapse. For 50 years, the iconic bridge had stood up to the ever-increasing traffic, a testament to the strength of its pre-stressed concrete and cable stays. So what went wrong that fateful day?