Leonardo da Vinci designed the viola organista, a keyboard instrument that used rotating wheels to bow strings.
Leonardo’s surviving drawings show a keyboard connected to strings and rotating wheels. Pressing keys selected the strings, while the moving wheels acted somewhat like the bow of a violin. This mechanism was intended to produce sustained tones without a player manually drawing a bow across each string.
The viola organista was never completed by Leonardo, so its exact sound and practical performance cannot be known from his drawings alone. Modern builders have made reconstructions based on the designs, allowing musicians to test the concept.
It is sometimes confused with an organ because of its name and keyboard. Unlike a conventional pipe organ, however, the design creates sound from bowed strings rather than air passing through pipes.