What instrument did Leonardo da Vinci design that used a keyboard and moving bows?

Leonardo da Vinci designed the viola organista, a keyboard instrument with moving bows.

The instrument combined features of a keyboard and a bowed string instrument. Pressing keys selected strings, while a mechanism moved one or more wheels or bows against them to produce sustained tones. Leonardo drew several versions, including one in the Codex Atlanticus.

Unlike a conventional organ, the viola organista was not primarily an air-powered instrument. Unlike a piano, its strings were not struck by hammers. Its sound-producing mechanism was closer in principle to a hurdy-gurdy, but the keyboard allowed a player to choose notes more directly.

No known surviving original instrument built by Leonardo has been identified. Modern makers have constructed playable reconstructions from his drawings, though the sketches leave some mechanical details open to interpretation. The design illustrates Leonardo's interest in combining musical performance with complex machinery.