Leonardo da Vinci sketched a ball bearing that used rolling balls between rings.
The purpose of the design was to reduce friction between moving parts. Instead of allowing two surfaces to slide directly against each other, the balls would roll between them, making rotary motion easier. Leonardo’s sketches show an early form of the principle used in many later machines.
The concept was not a modern sealed bearing. Leonardo also recognized a practical problem: if the balls touched one another, they could rub, crowd, and interfere with smooth movement. His notes include cage-like ideas intended to keep the balls separated, an important feature of later bearing designs.
Modern ball bearings are manufactured to precise tolerances and use hardened materials, lubrication, and seals. Leonardo’s contribution was an early systematic exploration of rolling-element friction, not the invention of the complete industrial bearing used today.