Leonardo da Vinci sketched a ball bearing using balls between two rings.
The arrangement was intended to reduce friction between moving surfaces. Instead of allowing one surface to slide directly against another, the balls roll between them. Rolling contact generally produces less resistance than sliding contact, making the principle useful for rotating shafts and other machinery.
Leonardo’s drawing is often cited as an early ball-bearing design, but it was not the first known use of rolling elements in every historical sense. Ancient and medieval machines used rollers and other low-friction arrangements, and practical industrial bearings developed much later with improved materials and manufacturing.
The balls in Leonardo’s sketch were also arranged in a way that would limit unwanted rubbing between adjacent balls. The concept is therefore more than a simple collection of loose spheres: it shows an attempt to manage friction systematically inside a machine.