Leonardo da Vinci is often credited with sketching an early ball bearing.
Around 1498, Leonardo drew diagrams showing balls placed between concentric rings so that one surface could rotate with less friction against another. The arrangement resembles the basic principle of a modern ball bearing: rolling elements separate moving surfaces and reduce sliding friction.
The idea was important because friction was a major engineering problem in machines. Leonardo also tried to prevent the balls from bunching together, showing that he understood a practical limitation of the simple design.
Leonardo did not invent the general idea of rolling objects to reduce friction; ancient civilizations used rollers, and earlier bearing-like devices existed. His importance lies in the detailed mechanical study and in recognizing how individual balls could be arranged within a bearing assembly.