What unusual musical instrument did Leonardo da Vinci design with bows moved by a wheel?

Leonardo da Vinci designed the viola organista, a keyboard instrument whose strings were sounded by rotating wheels and friction.

The instrument combined a keyboard with a mechanism resembling the bowing action used by string players. Pressing keys selected strings, while a wheel or wheels turned continuously and rubbed against them, producing sustained tones. Leonardo explored the concept in several drawings during the late fifteenth and early sixteenth centuries.

No original Leonardo viola organista is known to survive. Modern builders have constructed playable reconstructions based on his sketches, showing how the idea could produce sound while still differing from a conventional piano.

The viola organista is often confused with the hurdy-gurdy because both use a rotating wheel. The hurdy-gurdy uses a wheel turned by a crank and normally has keys or tangents for stopping strings; Leonardo’s design uses a keyboard and a distinct bowing mechanism.