Leonardo da Vinci studied a ball bearing, using rolling spheres to reduce friction between moving surfaces.
His sketches from around 1498 show balls arranged inside a ring so that they could roll rather than slide. That arrangement illustrates the basic principle of a bearing: rolling contact generally creates less friction than sliding contact. The drawings are among the earliest known depictions of a bearing using balls.
Leonardo’s design was not a modern sealed bearing. The balls were not fully separated in the way later cages separate them, and the sketch may have been part of his broader investigations into mechanics rather than a finished machine intended for manufacture.
Modern ball bearings are used in bicycles, electric motors, turbines, machine tools, and many other devices. Leonardo’s drawing therefore represents an important mechanical idea, but it should not be described as the first complete modern bearing.