What musical instrument did Leonardo da Vinci design with keys and a bow mechanism?

Leonardo da Vinci designed the viola organista, a keyboard instrument using bowed strings.

The viola organista combined features of a keyboard and a string instrument. Pressing a key selected a string, while rotating wheels covered with horsehair or another friction material rubbed against the strings to produce sound. In principle, it could create sustained tones while allowing a player to control several pitches from a keyboard.

Leonardo sketched versions of the instrument in his notebooks during the late fifteenth and early sixteenth centuries. No confirmed original instrument survives, so its exact construction and musical capabilities must be inferred from the drawings and notes.

The invention is often confused with a conventional organ because of its name and keyboard. It did not produce sound by sending air through pipes. It also was not simply a piano: the sound came from bowed strings rather than hammers striking strings. Modern builders have made playable reconstructions based on Leonardo's designs.