What musical instrument did Leonardo da Vinci design with a keyboard and a rotating bow?

Leonardo da Vinci designed the viola organista with a keyboard and a rotating bow mechanism.

Pressing a key in the design would bring a moving wheel or bow into contact with a string. The resulting friction was intended to create a sustained tone, while the keyboard gave the performer control over which strings sounded.

Leonardo’s drawings show that he was exploring a hybrid between keyboard instruments and bowed string instruments. The viola organista was therefore more than a decorative curiosity: it addressed the problem of producing continuous tones without requiring the player to move a bow by hand.

Some accounts call it an organ because its keyboard resembles that of an organ. However, it does not generate sound through organ pipes. Its strings and friction mechanism place it closer in principle to bowed instruments, even though its performance interface is a keyboard.