Leonardo da Vinci studied a ball-bearing concept using rolling balls to reduce friction between moving surfaces. His drawings show balls arranged so that they could move independently rather than jam against one another.
The principle is straightforward: rolling contact generally creates less resistance than sliding contact. A bearing based on that idea can support a rotating shaft or moving load while reducing friction and wear.
Leonardo’s studies date to the late 15th or early 16th century, but historians should distinguish a drawing from a manufactured, standardized bearing. Ancient and medieval engineers had used rollers and related friction-reducing devices, so Leonardo was not necessarily the first person to imagine rolling support.
The design is also different from a gear. Gears transmit motion through toothed wheels, while bearings support movement and reduce friction. Leonardo’s bearing study is notable because it addressed the practical problem of keeping rolling elements separated inside a mechanism.