What instrument did Leonardo da Vinci design with rotating bows rubbing strings?

Leonardo da Vinci designed the viola organista, an instrument using rotating bows to rub strings.

The viola organista combined features of a keyboard and a bowed string instrument. Pressing keys selected strings, while a rotating wheel or series of wheels supplied continuous friction through bowing surfaces. This arrangement allowed a performer to control pitch from a keyboard while producing a sustained, string-like sound.

Leonardo drew several versions during the late fifteenth and early sixteenth centuries, but he did not leave a surviving finished instrument. Modern builders have reconstructed versions from his sketches, showing that the concept can work even though the original design was never commercially developed.

The name can cause confusion because the instrument is neither a conventional viola nor an organ. It is best understood as a keyboard-controlled bowed-string invention.