The Bessemer process, patented by Henry Bessemer, was the first inexpensive industrial process for the mass production of steel from molten pig iron. By blowing air through the molten iron to burn off impurities, the process allowed for the creation of high-quality steel in large quantities and at a fraction of the previous cost. Steel is stronger and more flexible than iron, and its availability sparked a second industrial revolution. It enabled the construction of massive bridges, the skyscrapers that define modern cities, and the expansion of railways that connected continents. This invention made the modern urban landscape possible and fueled the growth of the manufacturing and construction industries throughout the late 19th and early 20th centuries.