What instrument did Leonardo da Vinci design with a rotating bow mechanism?

Leonardo da Vinci designed the viola organista with a rotating bow mechanism.

The proposed instrument combines features of a keyboard and bowed string instrument. Pressing keys would select strings, while a continuously rotating wheel or belt coated with horsehair would rub against them and produce sound.

Leonardo sketched several versions, probably during the late fifteenth or early sixteenth century. Unlike a conventional violin, the performer would not move a bow by hand; the keyboard would control which strings sounded.

No instrument built by Leonardo is known to survive. Modern makers have constructed working interpretations from his drawings, but these reconstructions should not be confused with a single definitive original model.