Leonardo da Vinci sketched a ball bearing that used rollers to reduce friction between moving surfaces.
His late-fifteenth-century bearing concept placed balls inside a ring-like assembly so that the balls could roll rather than slide. Rolling contact produces less friction than sliding contact, allowing a shaft or another moving part to turn more easily. Leonardo appears to have been investigating the problem while developing machines with rotating components.
The sketch is frequently described as an early ball-bearing design, but it was not a modern sealed bearing. Leonardo’s arrangement did not fully solve the problem of keeping the balls separated, and practical bearings require careful choices of materials, lubrication, tolerances, and protection from dirt.
Ball bearings became important in later industrial machinery, bicycles, motors, and other rotating systems. Leonardo’s contribution was a clear mechanical insight recorded centuries before precision manufacturing made durable, mass-produced bearings practical.