What instrument did Leonardo da Vinci design that combines a keyboard with bowed strings?

Leonardo da Vinci designed the viola organista, a keyboard instrument that uses bowed strings.

Leonardo drew several versions of the instrument in his notebooks, especially the Codex Atlanticus. Pressing keys was intended to select strings while a continuously moving wheel or belt supplied the bowing action. This gave the player a keyboard layout but a sound related to bowed string instruments.

The viola organista was never completed by Leonardo as a working historical instrument. Modern makers have built playable reconstructions from his drawings, although they differ in engineering details. It is sometimes confused with a hurdy-gurdy because both use a wheel to create continuous friction, but the viola organista is keyboard-controlled. Leonardo’s design also belongs to his broader interest in translating familiar musical mechanisms into new machines.