Leonardo da Vinci sketched a ball bearing using freely rotating balls between surfaces.
Around 1498, while studying friction and machine mechanisms, Leonardo drew a device in which balls separated moving parts. The balls were intended to reduce sliding friction by replacing it with rolling contact, a principle central to modern bearings.
The sketch is often credited as an early ball-bearing concept, but Leonardo was not the first person in history to use rolling elements in mechanisms. Earlier devices used rollers or balls, and later engineers developed bearings into practical standardized components.
Leonardo’s design also raises an engineering issue: without a cage or separator, the balls could bunch together and rub. Modern ball bearings use carefully shaped races and separators to keep the elements spaced. The drawing is important because it clearly applies rolling motion to reduce friction in machinery.