What stringed instrument did Leonardo da Vinci design to play automatically?

Leonardo da Vinci designed the viola organista, a keyboard instrument that produces sound with bowed strings.

The instrument combines features of a keyboard and a stringed instrument. Pressing keys selects notes, while a rotating mechanism moves a continuous belt or wheel against the strings, creating friction much like a bow.

Leonardo drew several versions of the idea in his notebooks during the fifteenth and sixteenth centuries. Unlike a conventional violin, the viola organista lets a player control pitches from a keyboard while the mechanism supplies the bowing action.

No surviving original instrument by Leonardo is known. Modern makers have built reconstructions from his drawings, showing that the concept can produce musical tones, although the historical design was never established as a standard instrument.