What stringed keyboard instrument did Leonardo da Vinci design to imitate a bowed ensemble?

Leonardo da Vinci designed the viola organista to imitate a bowed ensemble through a keyboard mechanism.

The viola organista was one of Leonardo’s most ambitious musical inventions. Its keyboard controlled strings that were rubbed by continuously moving wheels. Because the wheels kept moving while the player selected notes, the instrument could produce a sustained tone more like a viol or violin than the plucked sound of a harpsichord.

Leonardo explored multiple arrangements in his notebooks rather than producing one universally fixed model. Some versions used a belt carrying bowing material, while others used rotating wheels. This variation is why modern descriptions can differ in mechanical detail while still referring to the same family of designs.

The name is modern and descriptive, not necessarily a name Leonardo himself used for a completed instrument. The design is historically important because it anticipated later attempts to combine the expressive sound of bowed strings with the control and polyphony of a keyboard.