Leonardo da Vinci designed an early ball bearing using balls to reduce friction between moving surfaces.
Around 1498, while studying mechanical systems, Leonardo sketched a bearing arrangement in which balls moved between rings. The balls separated the surfaces, replacing much of the sliding friction with rolling friction. That principle is the foundation of modern ball bearings used in machines, vehicles, tools, and electrical motors.
Leonardo did not invent every form of bearing, and ancient engineers had used rollers and other methods to move heavy objects. His importance lies in clearly recording a practical ball-bearing arrangement and recognizing that the balls had to remain separated so they would not bunch together.
The sketch was not a modern sealed bearing. It lacked many features later developed by bearing makers, including standardized races, cages, seals, and precision manufacturing. Calling it an early ball-bearing concept is more accurate than claiming Leonardo produced the first complete modern bearing.