Leonardo da Vinci designed the viola organista, a keyboard instrument using a continuously bowed string mechanism.
Leonardo explored the design during the late 15th and early 16th centuries. The instrument combined features of a keyboard and bowed string instruments: pressing keys selected strings, while rotating wheels or belts rubbed against them to create sound. This allowed the player to control pitch from a keyboard while producing a sustained, string-like tone.
Several versions appear in Leonardo’s notebooks, showing that he continued refining the idea. The design is often described as an attempt to combine the expressive sound of a bowed instrument with the control of a keyboard.
Leonardo’s viola organista should not be confused with a conventional pipe organ, which produces sound through air flowing through pipes. It was also not a normal viola, because it was played with keys rather than a bow held by the performer. No surviving Renaissance example is known, but modern builders have reconstructed versions from his drawings.