Leonardo da Vinci designed the viola organista, an instrument that used a rotating bow to sound strings continuously.
The viola organista combines ideas from bowed string instruments and keyboard instruments. Pressing keys would select strings, while a rotating wheel or belt covered with horsehair would act like a bow. Because the bow could keep moving, the instrument was intended to produce sustained tones without requiring a player to draw a bow back and forth by hand.
Leonardo sketched several versions during the late 15th and early 16th centuries, but he did not complete a known playable instrument. The design is sometimes confused with the clavichord or harpsichord because it has a keyboard, yet those instruments produce sound by striking or plucking strings. Modern builders have constructed working versions from Leonardo’s drawings, demonstrating the ingenuity of the mechanism while also showing the practical difficulties of tuning and maintaining many moving parts.