The story begins with the collapse of the Tay Bridge in 1879.  Seventy five people lost their lives in that accident and engineers wanted to reassure a shocked public of the safety of the rail system.  The result was the massively over-constructed cantilever structure in the above photo.

The Tacoma Narrows Bridge in Washington State is a more recent example.  While there were thankfully no casualties in that collapse, the spectacular video of "Gallopin' Gertie" is a painful reminder of what can happen when engineers underestimate the power of nature.

PBS has put together an excellent web page about bridge building.  More than just another dry recitation of bridge related facts, it is an interactive learning tool for science enthusiasts of all ages.

Take a look and improve your bridge knowledge.