There is nothing new about things breaking. Sticks and stones have always broken bones, and knappers learned long ago how to fracture stones to make flint knives and arrowheads. Galileo used Renaissance experience with broken-stone obelisks and wooden ships to motivate his research into the strength of materials. But it was the widespread industrial application of iron in the development of the railroads that brought the growth of cracks and the fracture of parts containing them to the attention of engineers. When an axle, rail, wheel, beam or bridge broke spontaneously, the result was often a spectacular accident accompanied by loss of life. It was important to understand the ultimate cause of such failures in order to build reliable railroad systems.