What musical instrument did Leonardo da Vinci design with strings bowed by a wheel?

Leonardo da Vinci designed the viola organista, a keyboard instrument whose strings were sounded by a rotating wheel.

The player would press keys, and the keys would activate mechanisms that brought strings into contact with a continuously turning wheel. In principle, the wheel functioned somewhat like the bow of a string instrument, producing sustained tones while the keyboard selected the pitches. Leonardo drew several versions of the idea in his notebooks during the late 15th and early 16th centuries.

The viola organista was not a normal viola and did not use the bow held by a violinist. It was a hybrid concept combining keyboard control with bowed-string sound production. Leonardo’s sketches vary in their arrangements, showing that he was refining the mechanism rather than documenting one finished model.

Modern builders have constructed playable replicas, but no original Leonardo instrument is known to survive. The design is therefore best understood as an inventive instrument concept rather than a mass-produced Renaissance product.