What musical instrument did Leonardo da Vinci redesign with a continuous rotating bow?

The musical instrument Leonardo da Vinci redesigned with a continuous rotating bow was the viola organista.

Leonardo’s version combined a keyboard with bowed strings. Pressing a key would select or stop a string, while a rotating wheel or belt rubbed against the strings to produce sound. This arrangement aimed to give a keyboard player the sustained, expressive quality associated with bowed instruments.

The concept appears in Leonardo’s notebooks, including the Codex Atlanticus. He made several related sketches rather than leaving one universally fixed final design. The instrument was never established as a standard Renaissance keyboard instrument, and no surviving original built by Leonardo is known.

Modern makers have constructed working replicas from the drawings. The viola organista is therefore best understood as an experimental keyboard-string instrument, not as a conventional viola and not as an organ with pipes.