Leonardo da Vinci designed the viola organista, a keyboard instrument whose strings were sounded by rotating wheels covered with horsehair. The performer pressed keys much like a keyboard player, while the wheels continuously bowed the strings.
Leonardo drew several versions of the instrument in notebooks during the late fifteenth and early sixteenth centuries. His aim was to combine the controllable pitch of a keyboard with the sustained, expressive sound of bowed string instruments such as the viola.
The viola organista was never built in Leonardo’s lifetime, and no single surviving drawing gives a fully finalized design. Modern makers have constructed working interpretations from his sketches. It is sometimes confused with a hurdy-gurdy because both use a wheel to excite strings, but the viola organista is played with a keyboard rather than a hand-cranked mechanism.