Leonardo da Vinci designed the viola organista, a keyed instrument with a rotating bow mechanism.
The instrument combined features of a keyboard and a bowed string instrument. Pressing keys selected notes, while wheels covered with horsehair or similar material rubbed against the strings to produce sustained sound. Leonardo explored versions of the idea in several notebooks during the late 15th and early 16th centuries.
Unlike a piano, the viola organista did not strike strings with hammers. Unlike a conventional violin, it did not require the player to move a bow by hand. This combination made it an unusual attempt to unite keyboard control with the continuous tone of bowed strings.
Leonardo’s instrument was not widely adopted in his lifetime. Modern builders have constructed working replicas based on his drawings, showing that the mechanism can produce music, but the historical sketches leave some construction details open to interpretation.