What did Leonardo da Vinci’s viola organista use to produce sound?

Leonardo da Vinci’s viola organista used friction wheels to produce sound.

The viola organista was a keyboard instrument Leonardo designed in the late fifteenth century. Pressing keys would select strings, while rotating wheels rubbed against them in a way comparable to a bow moving across a string.

The instrument combined features associated with a keyboard and a bowed string instrument. Unlike a conventional piano, its strings were not struck by hammers. Unlike a normal viol, the performer controlled pitch through keys rather than directly stopping the strings with fingers.

Leonardo never built a confirmed working version. Several modern makers have constructed instruments based on his drawings, showing that the mechanism can produce sound while also revealing the engineering challenges in keeping the rotating wheels and strings aligned.