What keyboard instrument did Leonardo da Vinci design to bow strings continuously?

Leonardo da Vinci designed the viola organista, a keyboard instrument that bows strings continuously.

The instrument combines a keyboard with the principle of a bowed string instrument. Pressing keys selects strings, while rotating wheels or a belt coated with friction material rub against them to produce sound. In concept, it could provide sustained tones without requiring a musician to move a bow directly across each string.

Leonardo explored several versions in notebooks during the late fifteenth and early sixteenth centuries. The design belongs to his broader interest in musical engineering, acoustics, and mechanical automation. Unlike a normal organ, it does not produce sound by sending air through pipes; unlike a piano, its strings are not struck by hammers.

No original Leonardo viola organista is known to survive. Modern builders have constructed working interpretations from his drawings, but these are reconstructions rather than preserved Renaissance instruments. The name refers to its combination of viola-like strings and organ-like keyboard control.