Leonardo da Vinci designed an early ball bearing using freely rotating spheres to reduce friction. His sketches show balls held between rings so that one surface could move more easily against another.
The purpose of the design was to prevent the balls from rubbing together and jamming. Leonardo’s arrangement included separators or cage-like features, an important detail because a bearing works best when its rolling elements remain spaced and controlled.
The drawing is often described as an early ball-bearing concept, not proof that Leonardo invented every form of bearing. Rolling elements had earlier precedents, and modern bearings use carefully manufactured materials and tolerances. Leonardo’s contribution is the clear Renaissance-era study of a practical anti-friction mechanism based on rolling rather than sliding.