What instrument did Leonardo da Vinci invent using a wheel to bow strings continuously?

Leonardo da Vinci invented the viola organista, a keyboard instrument whose strings were bowed by a rotating wheel.

The design combines features of a keyboard and a bowed string instrument. Pressing keys selected strings, while a continuously rotating wheel rubbed against them to produce sound. Leonardo drew several versions of the idea, including designs in the Codex Atlanticus and the Codex Madrid II.

The viola organista was not a standard Renaissance instrument and no surviving original built by Leonardo is known. Its name is modern and reflects the instrument’s resemblance to viols and organs. Unlike a piano, which strikes strings with hammers, the viola organista uses friction from the wheel. Unlike a conventional violin, it allows a keyboard player to control pitches. Modern builders have reconstructed the instrument from Leonardo’s drawings, demonstrating that the mechanism can produce music.