Leonardo da Vinci designed the viola organista, a keyboard instrument that used rotating horsehair-covered wheels to sound strings.
The instrument was intended to combine features of a keyboard and bowed string instruments. Pressing keys selected strings, while a crank or other mechanism rotated friction wheels against them. The player could therefore control pitch with a keyboard while producing a sustained, bowed tone.
Leonardo drew several versions in his notebooks, especially in the Codex Atlanticus. He did not leave a confirmed surviving instrument from his own workshop, and the design remained largely theoretical during his lifetime. Modern builders have reconstructed versions from the drawings, though reconstructions differ in mechanical details.
The viola organista is sometimes confused with the hurdy-gurdy because both use rotating friction surfaces. The crucial difference is that Leonardo’s concept is keyboard-controlled, whereas a hurdy-gurdy normally uses keys to stop strings while a wheel acts as the bow.