What instrument did Leonardo da Vinci design using a continuous bow moved by keys?

Leonardo da Vinci designed the viola organista using a continuous bow moved by keys.

The instrument combined features of a keyboard and bowed string instrument. Pressing a key brought strings into contact with a rotating wheel or belt covered with horsehair, allowing sustained tones similar to those produced by a viol.

Leonardo made several drawings of related mechanisms, but no surviving instrument from his workshop is known. The concept was technically ambitious because it attempted to give a keyboard player the expressive sound of a bowed instrument.

The viola organista should not be confused with a conventional organ, harpsichord, or viola. Modern builders have constructed replicas from Leonardo’s drawings, making it possible to hear an interpretation of an instrument that remained theoretical in his era.