Structural work refers to the bones of a building—the steel beams and columns, the iron bars reinforcing the concrete in foundations, and the like. The work process has evolved since skyscrapers were first built in the 1880s using steel and poured concrete. At first, workers were able to continue to build these large structures using muscle and traditional hand tools, as we see in the early photographs here. But new machinery and new ideas of efficiency ultimately replaced some of the tools and many of the skilled occupations held by craftsmen.