Back then (to quote another comment here): "a quarter of all the bridges of any type built in the U.S. in the 1870's collapsed within ten years of their constru

Back then (to quote another comment here): "a quarter of all the bridges of any type built in the U.S. in the 1870's collapsed within ten years of their construction." Metallurgy was primitive, and there were no x-rays available to find hidden cracks formed during the manufacturing process.