August 29, 1907 - Over 3000 feet long, the Quebec Bridge crosses the lower Saint Lawrence River to the west of Quebec City, Canada. On this day it came crashing down.
The collapse happened while the bridge was under construction. There were some flaws in the original plans that allowed the load on the bridge to far exceed its carrying capacity. As construction continued, the builders started to notice some troubling deformations in the structure as it sagged and buckled under the mounting pressure.
A local engineer named Normal McClure expressed concern about the safety, but his superiors dismissed the issues as minor. As time went on the curving of previously straight steel beams forced the supervising engineer to telegraph an order that all construction halt until things could be sorted out. Unfortunately, the telegraph was sent too late in the day so it remained undelivered overnight.
Meanwhile, the workers on the bridge were ending their workday. As they gathered their tools and began to file off the bridge, disaster struck. Two massive sections of the bridge snapped off and plunged over 300 feet into the Saint Lawrence River. 75 of the 86 workers were killed.
A second attempt at constructing the bridge also collapsed in 1911 and 13 more workers died. Finally, in 1917 the bridge was completed and opened for rail traffic.
With a 1000-foot-long center span, it is still the longest cantilevered bridge span in the world.