What mechanical musical instrument did Leonardo da Vinci design using a rotating bow?

Leonardo da Vinci designed the viola organista, a mechanical musical instrument using a rotating bow.

The viola organista combines ideas from bowed string instruments and keyboard instruments. Pressing keys selects strings, while a continuously rotating wheel or belt rubs against them like a bow. This arrangement allowed the player to produce sustained bowed tones from a keyboard, rather than stopping and starting each note with a separate bow stroke.

Leonardo drew several versions of the instrument in notebooks, but there is no evidence that he completed a functioning version during his lifetime. Modern builders have constructed playable replicas from his drawings, though the surviving sketches leave room for interpretation. The instrument is not the same as a piano or a conventional organ: its sound comes from strings activated by friction, while its keyboard controls which strings are sounded. Its name refers to the viola-like tone Leonardo sought to create.