What keyboard instrument did Leonardo da Vinci design to make sustained string sounds?

Leonardo da Vinci designed the viola organista, a keyboard instrument that produces string sounds with rotating wheels.

The player presses keys, while a mechanism brings rosined wheels into contact with strings. The wheels act somewhat like the bow of a string instrument, allowing notes to be sustained while the keyboard controls pitch. Leonardo drew several versions of the concept in his notebooks.

The viola organista was never completed by Leonardo as a standard working instrument. It combines features associated with keyboard instruments and bowed strings, so it is sometimes described as a hybrid rather than as a conventional piano or organ.

Modern builders have constructed playable reconstructions from Leonardo’s drawings. These instruments demonstrate the underlying principle, but they do not prove that Leonardo’s original sketches contained every detail needed for immediate construction.