In 1856, Henry Bessemer patented a process that allowed for the mass production of steel from molten pig iron. By blowing air through the molten iron to burn off impurities (like carbon and silicon), the Bessemer converter made steel—which was previously expensive and produced in small batches—cheap and plentiful. This was the 'Age of Steel.' Steel was stronger and more flexible than iron, making it the essential material for the skyscrapers, suspension bridges, and massive naval ships that defined the late 19th and early 20th centuries. The process decreased the cost of steel by over 80%, allowing the railroad industry to replace brittle iron rails with durable steel ones, vastly increasing the safety and speed of transportation.