Leonardo da Vinci sketched a ball bearing using spheres to reduce friction between moving surfaces.
Around 1498, Leonardo made drawings of a device in which balls were separated so they would not rub directly against one another. The arrangement illustrates the basic principle of a bearing: rolling contact can replace much of the sliding friction found when two surfaces move directly against each other.
Leonardo did not create the modern standardized ball bearing used in machines today. His drawing is best understood as an early recorded design or conceptual step in the history of rolling bearings. Later engineers developed cages, races, hardened materials, and precision manufacturing.
The design is sometimes described as the invention of the ball bearing, but modern bearing technology emerged gradually over centuries. Leonardo’s importance lies in documenting the principle clearly during the Renaissance.