Leonardo da Vinci designed a rolling mill for reducing metal into thin sheets.
A rolling mill passes metal between rotating cylinders, compressing it and reducing its thickness. Leonardo’s drawings show an early concept for applying this controlled mechanical action to metalworking. The design demonstrates his interest in replacing irregular hammering with a more continuous and repeatable process.
The idea was not equivalent to a modern steel mill. Renaissance metallurgy used different materials, power sources, and production scales, and Leonardo’s surviving drawings do not establish that he built an industrial rolling line. They do, however, show a clear understanding of rollers as a way to shape metal.
A rolling mill is different from a forge, where heat and hammering or pressing shape metal. It is also different from wire drawing, which pulls metal through a die to reduce its diameter.