What musical instrument did Leonardo da Vinci design with strings controlled by keys?

Leonardo da Vinci designed the viola organista, a keyboard instrument with strings controlled by keys. Rotating wheels or bows were meant to rub the strings, producing a sustained sound while the keyboard selected the notes.

Leonardo explored the idea in several notebook sketches during the late fifteenth and early sixteenth centuries. The instrument combined the keyboard layout of an organ or harpsichord with the sound-producing friction of bowed string instruments. Its design shows his interest in adapting mechanical motion to music.

The viola organista was not a conventional viola, because a viola is played with a handheld bow. It was also not an organ, because it did not produce sound through pipes. No original Leonardo-built instrument is known to survive, but modern builders have created working interpretations from his drawings.