What Leonardo da Vinci musical instrument used rotating wheels to bow strings continuously?

Leonardo da Vinci’s viola organista used rotating wheels to bow strings continuously.

The instrument combined features of a keyboard and a bowed string instrument. Pressing keys selected strings, while rotating wheels rubbed against them to produce sustained tones. This allowed one player to control the pitches from a keyboard while obtaining a sound associated with bowed strings.

Leonardo developed several sketches for the idea during the Renaissance, but no known original instrument built by him survives. Modern makers have constructed working versions based on his drawings and related historical evidence.

The viola organista is not simply a conventional viola or an organ. Its name describes the hybrid concept: viola-like strings and keyboard-organ-style control, with mechanical wheels replacing a player’s bow.