‘Iron and steel’ explains how the Iron Bridge in Shropshire, UK, completed in 1779, illustrates the industrial cultures where modern architecture started to form. It indicates the beginnings of a shift in global culture, over two centuries, from artisan manufacturing towards mass production. The association of technology with progress became inseparable from modernity. Engineers such as Gustave Eiffel and Joseph Paxton reimagined iron as structural framing that could define the spaces of buildings. The development of less brittle steel resulted in new steel frameworks allowing walls—no longer loadbearing—to become separated conceptually from the building’s structure. The work of influential architects Frank Lloyd Wright and Ludwig Mies van der Rohe is also discussed.