Leonardo da Vinci is credited with an early ball-bearing design using balls to reduce friction between moving parts.
Leonardo studied ball bearings while developing mechanical systems in the late 15th century. His sketches show balls placed between rings so that one surface could rotate more easily relative to another. The balls replaced much of the sliding friction with rolling motion, an idea central to modern bearings.
The credit requires precision: Leonardo did not invent every form of rolling bearing, and ancient and medieval engineers used related rollers and rotating devices. His importance is that his surviving studies clearly describe and illustrate a practical ball-bearing arrangement. The design was not necessarily manufactured in large numbers during his lifetime.
Modern ball bearings use carefully shaped races, hardened balls, cages, and lubricants. Leonardo’s concept was simpler, but it addressed the same basic engineering problem: reducing energy loss and wear where parts rotate against one another.