What instrument did Leonardo da Vinci design by combining a keyboard with a bow?

Leonardo da Vinci designed the viola organista by combining a keyboard with a bow.

The viola organista was a keyboard instrument that Leonardo sketched in several notebooks, especially the Codex Atlanticus. Pressing keys would cause rotating wheels or a continuous bowing mechanism to touch strings, producing sustained tones. In concept, it combined features associated with bowed string instruments and keyboard instruments.

Leonardo never completed a surviving working version, and the instrument had no established Renaissance performance tradition. Its design is sometimes confused with a hurdy-gurdy because both use rotating friction to sound strings, but the viola organista is controlled by a keyboard. Modern builders have created playable reconstructions from Leonardo’s drawings, demonstrating the originality of his attempt to make bowed-string sound easier to control melodically.