Which unusual instrument did Leonardo da Vinci design using rotating wheels to bow strings?

Leonardo da Vinci designed the viola organista using rotating wheels to bow strings.

The viola organista combines ideas from bowed string instruments and keyboard mechanisms. Pressing keys was intended to bring strings into contact with rotating, rosined wheels, producing sustained tones without a player directly moving a bow across each string.

Leonardo drew several versions of the concept during the fifteenth and early sixteenth centuries. No authenticated original instrument built by Leonardo is known to survive, so the invention is reconstructed from his notebooks rather than from a preserved machine.

The instrument is often mistaken for an organ because of its keyboard and name. However, its sound-producing principle is based on bowed strings, not pipes. Modern builders have made working versions, including an instrument constructed by Slawomir Zubrzycki and presented publicly in the twenty-first century.