Leonardo da Vinci designed the viola organista, a mechanical instrument using rotating bow wheels.
The viola organista combined features of a keyboard instrument and bowed strings. Pressing keys selected strings, while rotating wheels covered with horsehair or another friction material acted as continuous bows. This arrangement was intended to let the performer sustain tones in a way that ordinary keyboard instruments could not.
Leonardo drew several versions of the concept, especially in manuscripts from the late fifteenth and early sixteenth centuries. The instrument was never known to have been completed by Leonardo, and no original example survives.
The viola organista is often confused with the hurdy-gurdy because both use rotating friction surfaces. The difference is that the hurdy-gurdy normally uses a hand-cranked wheel and keys to stop strings, whereas Leonardo’s design was conceived as a keyboard-controlled bowed-string instrument.