Leonardo da Vinci studied a ball bearing using spheres to reduce friction between moving surfaces. His sketches show balls positioned so that components could move with less sliding contact.
Leonardo’s bearing studies date to the late 15th or early 16th century and are associated with his work on machines, gears, and rotating mechanisms. The central idea is the same principle used in modern rolling-element bearings: rolling generally produces less resistance than sliding. His notes and drawings include arrangements of balls and cages intended to keep the elements separated.
Leonardo did not invent every form of bearing, and ancient devices had already used rollers and other methods to reduce friction. His importance lies in developing and recording a recognizable ball-bearing concept during the Renaissance. Modern bearings require precise materials, lubrication, tolerances, and manufacturing. Leonardo’s sketches were engineering studies rather than evidence of mass-produced components, so calling them modern bearings without qualification can overstate what the drawings demonstrate.