Leonardo da Vinci designed the viola organista, a keyboard instrument using rotating wheels to bow strings.
The instrument combined a keyboard with a mechanism inspired by bowed string instruments. Pressing keys selected strings, while rotating wheels or wheel-like surfaces provided continuous friction against them. This allowed one player to control several bowed sounds from a keyboard.
Leonardo drew versions of the idea in his notebooks, but no surviving original instrument from his workshop is known. The concept belongs to his wider interest in combining music, mechanics, and automation.
The viola organista is sometimes confused with an organ because of its name and keyboard. It does not create sound by sending air through ordinary organ pipes. It is closer in principle to a mechanically bowed string instrument, although its keyboard layout gives it a different playing method from a violin or viola.