What musical instrument did Leonardo da Vinci design using bows moved by rotating wheels?

Leonardo da Vinci designed the viola organista, a keyboard instrument whose strings were sounded by rotating, rosined wheels. His notebooks contain several related designs, showing his interest in combining keyboard control with the sustained sound of bowed strings.

When a player pressed a key, a mechanism could bring a string into contact with a rotating wheel. The wheel acted somewhat like the bow of a string instrument, allowing notes to continue while the wheel turned. The design was never documented as a completed Renaissance instrument built by Leonardo himself.

The viola organista combined ideas from the organ, harpsichord, and bowed instruments. Unlike a standard pipe organ, it produced sound from strings; unlike a violin, it used a keyboard to select pitches.

Modern builders have made reconstructions based on Leonardo's drawings. The name can cause confusion because the instrument is not a conventional viola and does not use the modern electronic meaning of “organista.”