Leonardo da Vinci drew a ball-bearing mechanism with two rings of balls to reduce friction between moving surfaces. His sketches, made around 1498, show balls held in a cage so they would roll rather than slide against one another.
The principle is the same as in modern rolling-element bearings: rolling contact normally creates less friction than sliding contact. Leonardo’s cage is especially notable because uncaged balls could bunch together and lose the intended spacing. His drawing is evidence of an early bearing concept, not proof that he manufactured standardized bearings.
Ancient and medieval machines used rollers and other low-friction devices before Leonardo. Industrial ball bearings became practical much later, with improved steel, precision manufacturing, and sealed designs. Thus Leonardo anticipated a key arrangement but did not create the modern bearing industry.